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  • Hot to get generic type from object type

    - by Murat
    My Classes are; class BaseClass { } class DerivedClass1 : BaseClass { } class GenericClass<T> { } class DerivedClass2 : BaseClass { GenericClass<DerivedClass1> subItem; } I want to access all fields of DerivedClass2 class. I use System.Reflection and FieldInfo.GetValue() method; Bu I cant get subItem field. FieldInfo.GetValue() method return type is "object". And I cant cast to GenericClass<DerivedClass1> or I cant get DerivedClass1 type. I try this with BaseClass BaseClass instance = FieldInfo.Getvalue(this) as GenericClass<BaseClass>; but instance is null. How to get instance with type or how to get only type?

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  • Scala type system : basic type mismatch

    - by SiM
    I have a basic type system type mismatch problem: I have a class with a method def Create(nodeItem : NodeItem) = {p_nodeStart.addEndNode(nodeItem)} where p_nodeStart is NodeCache class NodeCache[END_T<:BaseNode] private(node: Node) extends BaseNode { def addEndNode(endNode : END_T) = {this.CACHE_HAS_ENDNODES.Create(endNode)} and the error its giving me is: error: type mismatch; found : nodes.NodeItem required: Nothing def Create(nodeItem : NodeItem) = {p_nodeStart.addEndNode(nodeItem)} while the NodeCache is defined as object NodeTrigger { def Create() { val nodeTimeCache = NodeCache.Create[NodeItem](node) and in object NodeCache object NodeCache { def Create[END_T<:BaseNode]() { val nodeCache = new NodeCache[END_T](node); Any ideas, how to fix the error?

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  • A follow up on type coercion in C++, as it may be construed by type conversion

    - by David
    This is a follow up to my previous question. Consider that I write a function with the following prototype: int a_function(Foo val); Where foo is believed to be a type defined unsigned int. This is unfortunately not verifiable for lack of documentation. So, someone comes along and uses a_function, but calls it with an unsigned int as an argument. Here the story takes a turn. Foo turns out to actually be a class, which can take an unsigned int as a single argument of unsigned int in an explicit constructor. Is it a standard and reliable behavior for the compiler to render the function call by doing a type conversion on the argument. I.e. is the compiler supposed to recognize the mismatch and insert the constructor? Or should I get a compile time error reporting the type mismatch.

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  • Which statically typed languages support intersection types for function return values?

    - by stakx
    Initial note: This question got closed after several edits because I lacked the proper terminology to state accurately what I was looking for. Sam Tobin-Hochstadt then posted a comment which made me recognise exactly what that was: programming languages that support intersection types for function return values. Now that the question has been re-opened, I've decided to improve it by rewriting it in a (hopefully) more precise manner. Therefore, some answers and comments below might no longer make sense because they refer to previous edits. (Please see the question's edit history in such cases.) Are there any popular statically & strongly typed programming languages (such as Haskell, generic Java, C#, F#, etc.) that support intersection types for function return values? If so, which, and how? (If I'm honest, I would really love to see someone demonstrate a way how to express intersection types in a mainstream language such as C# or Java.) I'll give a quick example of what intersection types might look like, using some pseudocode similar to C#: interface IX { … } interface IY { … } interface IB { … } class A : IX, IY { … } class B : IX, IY, IB { … } T fn() where T : IX, IY { return … ? new A() : new B(); } That is, the function fn returns an instance of some type T, of which the caller knows only that it implements interfaces IX and IY. (That is, unlike with generics, the caller doesn't get to choose the concrete type of T — the function does. From this I would suppose that T is in fact not a universal type, but an existential type.) P.S.: I'm aware that one could simply define a interface IXY : IX, IY and change the return type of fn to IXY. However, that is not really the same thing, because often you cannot bolt on an additional interface IXY to a previously defined type A which only implements IX and IY separately. Footnote: Some resources about intersection types: Wikipedia article for "Type system" has a subsection about intersection types. Report by Benjamin C. Pierce (1991), "Programming With Intersection Types, Union Types, and Polymorphism" David P. Cunningham (2005), "Intersection types in practice", which contains a case study about the Forsythe language, which is mentioned in the Wikipedia article. A Stack Overflow question, "Union types and intersection types" which got several good answers, among them this one which gives a pseudocode example of intersection types similar to mine above.

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  • kernel module compiling error

    - by wati
    sh@ubuntu:/home/ccpp/helloworld$ make gcc-4.6 -O2 -DMODULE -D_KERNEL_ -W -Wall -Wstrict-prototypes -Wmissing-prototypes -isystem /lib/modules/`uname -r`/build/include -c -o hello-1.o hello-1.c hello-1.c:4:0: warning: "MODULE" redefined [enabled by default] <command-line>:0:0: note: this is the location of the previous definition hello-1.c:6:0: warning: "_KERNEL_" redefined [enabled by default] <command-line>:0:0: note: this is the location of the previous definition In file included from /lib/modules/3.2.0-25-generic/build/include/linux/list.h:4:0, from /lib/modules/3.2.0-25-generic/build/include/linux/module.h:9, from hello-1.c:7: /lib/modules/3.2.0-25-generic/build/include/linux/types.h:13:2: warning: #warning "Attempt to use kernel headers from user space, see http://kernelnewbies.org/KernelHeaders" [-Wcpp] In file included from /lib/modules/3.2.0-25-generic/build/include/linux/module.h:9:0, from hello-1.c:7: /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘INIT_LIST_HEAD’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:26:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:27:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘__list_add’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:41:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:42:5: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:43:5: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:44:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_add’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:62:28: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_add_tail’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:76:22: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘__list_del’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:88:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:89:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘__list_del_entry’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:101:18: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:101:31: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_del’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:106:18: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:106:31: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:107:7: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:108:7: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_replace’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:125:5: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:125:17: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:126:5: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:127:5: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:127:17: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:128:5: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_is_last’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:179:13: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_empty’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:188:13: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_empty_careful’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:206:31: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:207:40: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_rotate_left’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:219:15: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_is_singular’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:230:35: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:230:49: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘__list_cut_position’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:236:37: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:237:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:237:19: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:238:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:239:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:240:7: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:241:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:242:11: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_cut_position’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:265:8: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘__list_splice’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:277:32: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:278:31: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:280:7: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:281:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:283:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:284:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_splice’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:296:33: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_splice_tail’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:308:27: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_splice_init’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:322:33: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘list_splice_tail_init’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:339:27: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘INIT_HLIST_NODE’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:572:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:573:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘hlist_unhashed’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:578:11: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘hlist_empty’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:583:11: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘__hlist_del’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:588:29: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:589:31: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:592:7: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘hlist_del’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:598:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:599:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘hlist_add_head’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:612:30: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:613:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:615:8: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:615:20: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:616:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:617:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:617:15: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘hlist_add_before’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:624:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:624:17: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:625:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:626:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:626:18: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:627:5: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘hlist_add_after’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:633:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:633:16: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:634:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:635:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:635:18: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:637:9: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:638:7: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:638:29: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘hlist_add_fake’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:644:3: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:644:15: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h: In function ‘hlist_move_list’: /lib/modules/3.2.0-25-generic/build/include/linux/list.h:654:5: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:654:18: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:655:9: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:656:6: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:656:27: error: dereferencing pointer to incomplete type /lib/modules/3.2.0-25-generic/build/include/linux/list.h:657:5: error: dereferencing pointer to incomplete type In file included from /lib/modules/3.2.0-25-generic/build/include/linux/module.h:12:0, from hello-1.c:7: /lib/modules/3.2.0-25-generic/build/include/linux/cache.h: At top level: /lib/modules/3.2.0-25-generic/build/include/linux/cache.h:5:23: fatal error: asm/cache.h: No such file or directory compilation terminated. make: *** [hello-1.o] Error 1 i got this error after compiling an helloworld program my program is #define MODULE #define LINUX #define _KERNEL_ #include <linux/module.h> #include <linux/kernel.h> int init_module(void) { printk("<1>hello World 1.\n"); return 0; } void cleanup_module(void) { printk(KERN_ALERT "goodbye world 1.\n"); } MODULE_LICENSE("GPL"); my make file is: TARGET := hello-1 WARN := -W -Wall -Wstrict-prototypes -Wmissing-prototypes INCLUDE := -isystem /lib/modules/`uname -r`/build/include CFLAGS := -O2 -DMODULE -D_KERNEL_ ${WARN} ${INCLUDE} CC := gcc-4.6 ${TARGET}.o: ${TARGET}.c .PHONY: clean clean: rm -rf ${TARGET}.o iam usin kernel 3.2.0.25 as novice i can't able to figure out where the problem is I SEARCHED EVERY THING I CAN TO KNOW ABOUT THIS ERROR BUT I CANT UNDERSTAND &I GET IRRELEVANT DOCS anybody help me please

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  • How Can I Check an Object to See its Type and Return A Casted Object

    - by Russ Bradberry
    I have method to which I pass an object. In this method I check it's type and depending on the type I do something with it and return a Long. I have tried every which way I can think of to do this and I always get several compiler errors telling me it expects a certain object but gets another. Can someone please explain to me what I am doing wrong and guide me in the right direction? What I have tried thus far is below: override def getInteger(obj:Object) = { if (obj.isInstanceOf[Object]) null else if (obj.isInstanceOf[Number]) (obj:Number).longValue() else if (obj.isInstanceOf[Boolean]) if (obj:Boolean) 1 else 0 else if (obj.isInstanceOf[String]) if ((obj:String).length == 0 | (obj:String) == "null") null else try { Long.parse(obj:String) } catch { case e: Exception => throw new ValueConverterException("value \"" + obj.toString() + "\" of type " + obj.getClass().getName() + " is not convertible to Long") } }

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  • SQL SERVER – Summary of Month – Wait Type – Day 28 of 28

    - by pinaldave
    I am glad to announce that the month of Wait Types and Queues very successful. I am glad that it was very well received and there was great amount of participation from community. I am fortunate to have some of the excellent comments throughout the series. I want to dedicate this series to all the guest blogger – Jonathan, Jacob, Glenn, and Feodor for their kindness to take a participation in this series. Here is the complete list of the blog posts in this series. I enjoyed writing the series and I plan to continue writing similar series. Please offer your opinion. SQL SERVER – Introduction to Wait Stats and Wait Types – Wait Type – Day 1 of 28 SQL SERVER – Signal Wait Time Introduction with Simple Example – Wait Type – Day 2 of 28 SQL SERVER – DMV – sys.dm_os_wait_stats Explanation – Wait Type – Day 3 of 28 SQL SERVER – DMV – sys.dm_os_waiting_tasks and sys.dm_exec_requests – Wait Type – Day 4 of 28 SQL SERVER – Capturing Wait Types and Wait Stats Information at Interval – Wait Type – Day 5 of 28 SQL SERVER – CXPACKET – Parallelism – Usual Solution – Wait Type – Day 6 of 28 SQL SERVER – CXPACKET – Parallelism – Advanced Solution – Wait Type – Day 7 of 28 SQL SERVER – SOS_SCHEDULER_YIELD – Wait Type – Day 8 of 28 SQL SERVER – PAGEIOLATCH_DT, PAGEIOLATCH_EX, PAGEIOLATCH_KP, PAGEIOLATCH_SH, PAGEIOLATCH_UP – Wait Type – Day 9 of 28 SQL SERVER – IO_COMPLETION – Wait Type – Day 10 of 28 SQL SERVER – ASYNC_IO_COMPLETION – Wait Type – Day 11 of 28 SQL SERVER – PAGELATCH_DT, PAGELATCH_EX, PAGELATCH_KP, PAGELATCH_SH, PAGELATCH_UP – Wait Type – Day 12 of 28 SQL SERVER – FT_IFTS_SCHEDULER_IDLE_WAIT – Full Text – Wait Type – Day 13 of 28 SQL SERVER – BACKUPIO, BACKUPBUFFER – Wait Type – Day 14 of 28 SQL SERVER – LCK_M_XXX – Wait Type – Day 15 of 28 SQL SERVER – Guest Post – Jonathan Kehayias – Wait Type – Day 16 of 28 SQL SERVER – WRITELOG – Wait Type – Day 17 of 28 SQL SERVER – LOGBUFFER – Wait Type – Day 18 of 28 SQL SERVER – PREEMPTIVE and Non-PREEMPTIVE – Wait Type – Day 19 of 28 SQL SERVER – MSQL_XP – Wait Type – Day 20 of 28 SQL SERVER – Guest Posts – Feodor Georgiev – The Context of Our Database Environment – Going Beyond the Internal SQL Server Waits – Wait Type – Day 21 of 28 SQL SERVER – Guest Post – Jacob Sebastian – Filestream – Wait Types – Wait Queues – Day 22 of 28 SQL SERVER – OLEDB – Link Server – Wait Type – Day 23 of 28 SQL SERVER – 2000 – DBCC SQLPERF(waitstats) – Wait Type – Day 24 of 28 SQL SERVER – 2011 – Wait Type – Day 25 of 28 SQL SERVER – Guest Post – Glenn Berry – Wait Type – Day 26 of 28 SQL SERVER – Best Reference – Wait Type – Day 27 of 28 SQL SERVER – Summary of Month – Wait Type – Day 28 of 28 Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, PostADay, SQL, SQL Authority, SQL Optimization, SQL Query, SQL Scripts, SQL Server, SQL Tips and Tricks, SQL Wait Stats, SQL Wait Types, SQLServer, T SQL, Technology

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  • Is type safety worth the trade-offs?

    - by Prof Plum
    I began coding in in Python primarily where there is no type safety, then moved to C# and Java where there is. I found that I could work a bit more quickly and with less headaches in Python, but then again, my C# and Java apps are at much higher level of complexity so I have never given Python a true stress test I suppose. The Java and C# camps make it sound like without the type safety in place, most people would be running into all sorts of horrible bugs left an right and it would be more trouble than its worth. This is not a language comparison, so please do not address issues like compiled vs interpreted. Is type safety worth the hit to speed of development and flexibilty? WHY? to the people who wanted an example of the opinion that dynamic typing is faster: "Use a dynamically typed language during development. It gives you faster feedback, turn-around time, and development speed." - http://blog.jayway.com/2010/04/14/static-typing-is-the-root-of-all-evil/

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  • Comparison between a value with static type Array and a possibly unrelated type Class

    - by Kaoru
    I got this error: Comparison between a value with static type Array and a possibly unrelated type Class. After i modify the class to many classes (before that, everything is on 1 class (all of the functions)), but after i move everything to many classes (all the functions is not on 1 class), that error appear. How to solve this? I am using AS3 and as3isolib Library. Here is the code after i modify the function: if (Constant.dude.y < Constant._numY) { if (Constant.dude.sprites != marioBackClass) { Constant.dude.sprites = [marioBackClass]; Constant.dudeDir = "Up"; } } Here is the code before i change the function to many classes: if (dude.y < ._numY) { if (dude.sprites.toString() != marioBackClass.toString()) { dude.sprites = [marioBackClass]; dudeDir = "Up"; } }

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  • Haskell type signature with multiple type somethings (predicates?, for example Eq a =>)

    - by Andrew
    I'm not sure if type predicates is the right term, in fact I've never learned the word for this, so an edit to correct would be helpful - I'm referring to when you give the tipe of function f :: a -> b and you want to say a is a Eq and you say f :: Eq a => a -> b, the name for Eq a => - this is the thing i called a type predicate. My question, though, is how to have multiple of these, so if A is an Eq and B is a Num, I could say either f :: Eq a => a -> b or f :: Num b => a -> b. So, how can I have Eq a => and Num b => at the same time? f :: Eq a => Num b => a -> b, f :: Eq a -> Num b => a -> b, and f :: Eq a, Num b => a -> b all didn't do what I wanted.

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  • Help with possible Haskell type inference quiz questions

    - by Linda Cohen
    foldr:: (a -> b -> b) -> b -> [a] -> b map :: (a -> b) -> [a] -> [b] mys :: a -> a (.) :: (a -> b) -> (c -> a) -> c -> b what is inferred type of: a.map mys :: b.mys map :: c.foldr map :: d.foldr map.mys :: I've tried to create mys myself using mys n = n + 2 but the type of that is mys :: Num a => a -> a What's the difference between Num a = a - a and just a - a? Or what does 'Num a =' mean? Is it that mys would only take Num type? So anyways, a) I got [a] - [a] I think because it would just take a list and return it +2'd according to my definition of mys b) (a - b) - [a] - [b] I think because map still needs take both arguments like (*3) and a list then returns [a] which goes to mys and returns [b] c) I'm not sure how to do this 1. d) I'm not sure how to do this 1 either but map.mys means do mys first then map right? Are my answers and thoughts correct? If not, why not? THANKS!

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  • Convert List of one type to Array of another type using Dozer

    - by aheu
    I'm wondering how to convert a List of one type to an array of another type in Java using Dozer. The two types have all the same property names/types. For example, consider these two classes. public class A{ private String test = null; public String getTest(){ return this.test } public void setTest(String test){ this.test = test; } } public class B{ private String test = null; public String getTest(){ return this.test } public void setTest(String test){ this.test = test; } } I've tried this with no luck. List<A> listOfA = getListofAObjects(); Mapper mapper = DozerBeanMapperSingletonWrapper.getInstance(); B[] bs = mapper.map(listOfA, B[].class); I've also tried using the CollectionUtils class. CollectionUtils.convertListToArray(listOfA, B.class) Neither are working for me, can anyone tell me what I am doing wrong? The mapper.map function works fine if I create two wrapper classes, one containing a List and the other a b[]. See below: public class C{ private List<A> items = null; public List<A> getItems(){ return this.items; } public void setItems(List<A> items){ this.items = items; } } public class D{ private B[] items = null; public B[] getItems(){ return this.items; } public void setItems(B[] items){ this.items = items; } } This works oddly enough... List<A> listOfA = getListofAObjects(); C c = new C(); c.setItems(listOfA); Mapper mapper = DozerBeanMapperSingletonWrapper.getInstance(); D d = mapper.map(listOfA, D.class); B[] bs = d.getItems(); How do I do what I want to do without using the wrapper classes (C & D)? There has got to be an easier way... Thanks!

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  • Do any languages other than haskell/agda have a hindley-milner type system and type classes?

    - by Jimmy Hoffa
    In pondering what gives Haskell such a layer of mental pain in becoming proficient the main thing I can think of are the Monads, Applicatives, Functors, and gaining an intuition to know how a list or maybe will behave in regards to sequence or alternate or bind etc. But why haven't other languages presented these same concepts given the usefulness of monads/applicatives/etc? It occurs to me, type classes are the key, so the question is: Have any languages other than Haskell/Agda actually implemented type classes in the same or similar way?

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  • Webpage loading with wrong content-type after setting up CloudFlare

    - by Daniel Little
    I recently migrated my blog to the Ghost service, I've also setup an alias DNS record with CloudFlare. While showing the blog to a colleague I discovered one of the posts wasn't loading properly and would instead prompt to be downloaded with an application/octet-stream content-type. I can view all the pages without any issues and I believe we're both on the same network as well. Has anyone received a wrong content type like application/octet-stream using CloudFlare, or know what I can do to correct this?

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  • Why doesn't Haskell have type-level lambda abstractions?

    - by Petr Pudlák
    Are there some theoretical reasons for that (like that the type checking or type inference would become undecidable), or practical reasons (too difficult to implement properly)? Currently, we can wrap things into newtype like newtype Pair a = Pair (a, a) and then have Pair :: * -> * but we cannot do something like ?(a:*). (a,a). (There are some languages that have them, for example, Scala does.)

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  • Webservice Return Generic Result Type or Purposed Result Type

    - by hanzolo
    I'm building a webservice which returns JSON / XML / SOAP at the moment.. and I'm not entirely sure which approach for returning results is best. Which would be a better return value? A generic "transfer" type structure, which carries Generic properties or a purposed type with distinct properties: class GenericTransferObject{ public string returnVal; public string returnType; } VS class PurposedTransferObject_1{ public string Property1; } //and then building additional "types" for additional values class PurposedTransferObject_2 { public string PropertyA; public string PropertyB; } Now, this would be the serialized and returned from a web service call via some client technology, JQuery in this example. SO if I called: /GetDaysInWeek/ I would either get back: {"returnType": "DaysInWeek", "returnVal": "365" } OR {"DaysInWeek": "365"} And then it would go from there. On the one hand there's flexibilty with the 1st example. I can add "returnTypes" without needing to adjust the client other than referencing an additional "index".. but if I had to add a property, now i'm changing a structure definition.. Is there an obvious choice in this situation?

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  • Apache serving wrong Content-Type for Rails files

    - by NudeCanalTroll
    Apache keeps serving up my Rails files with a Content-Type of 'text/plain' in the header. I have mod_mime installed, a mime.types files with all the correct MIME assignments, and the following code in my configuration. Any thoughts? DefaultType text/plain <IfModule mime_module> TypesConfig /etc/apache2/mime.types AddType application/x-compress .Z AddType application/x-gzip .gz .tgz </IfModule>

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  • Is conditional return type ever a good idea?

    - by qegal
    So I have a method that's something like this: -(BOOL)isSingleValueRecord And another method like this: -(Type)typeOfSingleValueRecord And it occurred to me that I could combine them into something like this: -(id)isSingleValueRecord And have the implementation be something like this: -(id)isSingleValueRecord { //If it is single value if(self.recordValue = 0) { //Do some stuff to determine type, then return it return typeOfSingleValueRecord; } //If its not single value else { //Return "NO" return [NSNumber numberWithBool:NO]; } } So combining the two methods makes it more efficient but makes the readability go down. In my gut, I feel like I should go with the two-method version, but is that really right? Is there any case that I should go with the combined version?

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  • .NET Type Conversion Issue: Simple but difficult

    - by jaderanderson
    Well, the question is kinda simple. I have a object defined as: public class FullListObject : System.Collections.ArrayList, IPagedCollection And when i try to: IPagedCollection pagedCollection = (IPagedCollection)value; It don't work... value is a FullListObject... this is my new code trying to get around a issue with the "is" operator. When the system tests (value is IPagedCollection) it never gets true for FullListObject. How to cast the object to another object with a interface type?

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  • Type Object does not support slicing Unity3D

    - by Vish
    I am getting the following error in my code and I can't seem to understand why. Can anyone help me with it? This is my current code. The line causing the error is marked in a comment near the end. var rows : int = 4; var cols : int = 4; var totalCards : int = cols * rows; var matchesNeedToWin : int = totalCards * 0.5; var matchesMade : int = 0; var cardW : int = 100; var cardH : int = 100; var aCards : Array; var aGrid : Array; // This Array will store the two cards that the player flipped var aCardsFlipped : ArrayList; // To prevent player from clicking buttons when we don't want him to var playerCanClick : boolean; var playerHasWon : boolean = false; class Card extends System.Object { var isFaceUp : boolean = false; var isMatched : boolean = false; var img : String; function Card () { img = "robot"; } } function Start () { var i : int = 0; var j : int = 0; playerCanClick = true; aCards = new Array (); aGrid = new Array (); aCardsFlipped = new ArrayList (); for ( i = 0; i < rows; i++) { aGrid [i] = new Array (); for (j = 0; j < cols; cols++ ) { aGrid [i] [j] = new Card (); // <------ Error over here } } } function Update () { Debug.Log("Game Screen has loaded"); } The error states as follows: Error BCE0048: Type 'Object' does not support slicing. (BCE0048) (Assembly-UnityScript)

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  • Dynamically creating a Generic Type at Runtime

    - by Rick Strahl
    I learned something new today. Not uncommon, but it's a core .NET runtime feature I simply did not know although I know I've run into this issue a few times and worked around it in other ways. Today there was no working around it and a few folks on Twitter pointed me in the right direction. The question I ran into is: How do I create a type instance of a generic type when I have dynamically acquired the type at runtime? Yup it's not something that you do everyday, but when you're writing code that parses objects dynamically at runtime it comes up from time to time. In my case it's in the bowels of a custom JSON parser. After some thought triggered by a comment today I realized it would be fairly easy to implement two-way Dictionary parsing for most concrete dictionary types. I could use a custom Dictionary serialization format that serializes as an array of key/value objects. Basically I can use a custom type (that matches the JSON signature) to hold my parsed dictionary data and then add it to the actual dictionary when parsing is complete. Generic Types at Runtime One issue that came up in the process was how to figure out what type the Dictionary<K,V> generic parameters take. Reflection actually makes it fairly easy to figure out generic types at runtime with code like this: if (arrayType.GetInterface("IDictionary") != null) { if (arrayType.IsGenericType) { var keyType = arrayType.GetGenericArguments()[0]; var valueType = arrayType.GetGenericArguments()[1]; … } } The GetArrayType method gets passed a type instance that is the array or array-like object that is rendered in JSON as an array (which includes IList, IDictionary, IDataReader and a few others). In my case the type passed would be something like Dictionary<string, CustomerEntity>. So I know what the parent container class type is. Based on the the container type using it's then possible to use GetGenericTypeArguments() to retrieve all the generic types in sequential order of definition (ie. string, CustomerEntity). That's the easy part. Creating a Generic Type and Providing Generic Parameters at RunTime The next problem is how do I get a concrete type instance for the generic type? I know what the type name and I have a type instance is but it's generic, so how do I get a type reference to keyvaluepair<K,V> that is specific to the keyType and valueType above? Here are a couple of things that come to mind but that don't work (and yes I tried that unsuccessfully first): Type elementType = typeof(keyvalue<keyType, valueType>); Type elementType = typeof(keyvalue<typeof(keyType), typeof(valueType)>); The problem is that this explicit syntax expects a type literal not some dynamic runtime value, so both of the above won't even compile. I turns out the way to create a generic type at runtime is using a fancy bit of syntax that until today I was completely unaware of: Type elementType = typeof(keyvalue<,>).MakeGenericType(keyType, valueType); The key is the type(keyvalue<,>) bit which looks weird at best. It works however and produces a non-generic type reference. You can see the difference between the full generic type and the non-typed (?) generic type in the debugger: The nonGenericType doesn't show any type specialization, while the elementType type shows the string, CustomerEntity (truncated above) in the type name. Once the full type reference exists (elementType) it's then easy to create an instance. In my case the parser parses through the JSON and when it completes parsing the value/object it creates a new keyvalue<T,V> instance. Now that I know the element type that's pretty trivial with: // Objects start out null until we find the opening tag resultObject = Activator.CreateInstance(elementType); Here the result object is picked up by the JSON array parser which creates an instance of the child object (keyvalue<K,V>) and then parses and assigns values from the JSON document using the types  key/value property signature. Internally the parser then takes each individually parsed item and adds it to a list of  List<keyvalue<K,V>> items. Parsing through a Generic type when you only have Runtime Type Information When parsing of the JSON array is done, the List needs to be turned into a defacto Dictionary<K,V>. This should be easy since I know that I'm dealing with an IDictionary, and I know the generic types for the key and value. The problem is again though that this needs to happen at runtime which would mean using several Convert.ChangeType() calls in the code to dynamically cast at runtime. Yuk. In the end I decided the easier and probably only slightly slower way to do this is a to use the dynamic type to collect the items and assign them to avoid all the dynamic casting madness: else if (IsIDictionary) { IDictionary dict = Activator.CreateInstance(arrayType) as IDictionary; foreach (dynamic item in items) { dict.Add(item.key, item.value); } return dict; } This code creates an instance of the generic dictionary type first, then loops through all of my custom keyvalue<K,V> items and assigns them to the actual dictionary. By using Dynamic here I can side step all the explicit type conversions that would be required in the three highlighted areas (not to mention that this nested method doesn't have access to the dictionary item generic types here). Static <- -> Dynamic Dynamic casting in a static language like C# is a bitch to say the least. This is one of the few times when I've cursed static typing and the arcane syntax that's required to coax types into the right format. It works but it's pretty nasty code. If it weren't for dynamic that last bit of code would have been a pretty ugly as well with a bunch of Convert.ChangeType() calls to litter the code. Fortunately this type of type convulsion is rather rare and reserved for system level code. It's not every day that you create a string to object parser after all :-)© Rick Strahl, West Wind Technologies, 2005-2011Posted in .NET  CSharp   Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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  • Types in Haskell

    - by Linda Cohen
    I'm kind of new in Haskell and I have difficulty understanding how inferred types and such works. map :: (a -> b) -> [a] -> [b] (.) :: (a -> b) -> (c -> a) -> c -> b What EXACTLY does that mean? foldr :: (a -> b -> b) -> b -> [a] -> b foldl :: (a -> b -> a) -> a -> [b] -> a foldl1 :: (a -> a -> a) -> [a] -> a What are the differences between these? And how would I define the inferred type of something like foldr map THANKS!

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