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  • The question about the basics of LINQ to SQL working

    - by Alex
    I just started learning LINQ to SQL, and so far I'm impressed with the easy of use and good performance. I used to think that when doing LINQ queries like from Customer in DB.Customers where Customer.Age > 30 select Customer Get all customers from the database ("SELECT * FROM Customers"), move them to the Customers array and then make a search in that Array using .NET methods. This is very inefficient, what if there are hundreds of thousands of customers in the database? Making such big SELECT queries would kill the web application. Now after experiencing how actually fast LINQ to SQL is, I start to suspect that when doing that query I just wrote, LINQ somehow converts it to a SQL Query string SELECT * FROM Customers WHERE Age > 30 And only when necessary it will run the query. So my question is: am I right? And when is the query actually run? The reason why I'm asking is not only because I want to understand how it works in order to build good optimized applications, but because I came across the following problem. I have 2 tables, one of them is Books, the other has information on how many books were sold on certain days. My goal is to select books that had at least 50 sales/day in past 10 days. It's done with this simple query: from Book in DB.Books where (from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID).Contains(Book.ID) select Book The point is, I have to use the checking part in several queries and I decided to create an array with IDs of all popular books: var popularBooksIDs = from Sale in DB.Sales where Sale.SalesAmount >= 50 and Sale.DateOfSale >= DateTime.Now.AddDays(-10) select Sale.BookID; BUT when I try to do the query now: from Book in DB.Books where popularBooksIDs.Contains(Book.ID) select Book It doesn't work! That's why I think that we can't use thins kinds of shortcuts in LINQ to SQL queries, like we can't use them in real SQL. We have to create straightforward queries, am I right?

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  • If statement doesn't work? do download without filed name and email

    - by user1833871
    I've created some if / else statements to get a download when a user hit click jf he fields name and email but doesn"t work for my site http://my-easy-woodworking-projects.com because it is do download without field name and email contact.php is <?php $field_name = $_POST['cf_name']; $field_email = $_POST['cf_email']; $field_message = $_POST['cf_message']; $mail_to = '[email protected]'; $subject = 'Message from a site visitor '.$field_name; $body_message = 'From: '.$field_name."\n"; $body_message .= 'E-mail: '.$field_email."\n"; $body_message .= 'Message: '.$field_message; $headers = 'From: '.$field_email."\r\n"; $headers .= 'Reply-To: '.$field_email."\r\n"; $mail_status = mail($mail_to, $subject, $body_message, $headers); if ($mail_status) { echo <script>\n" echo "var str = \"download\"; \n"" echo "document.write(str.link("http://www.myshedplans.com/12BY8SHED.pdf"));\n" echo "</script>\n" } echo else { echo <script language="javascript" type="text/javascript"> echo // Print a message echo alert('Message failed. Please, send an email to [email protected]'); echo // Redirect to some page of the site. You can also specify full URL, e.g. http://template-help.com window.location = 'contact_page.html'; echo </script> }?>

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  • Can I write a test that succeeds if and only if a statement does not compile?

    - by Billy ONeal
    I'd like to prevent clients of my class from doing something stupid. To that end, I have used the type system, and made my class only accept specific types as input. Consider the following example (Not real code, I've left off things like virtual destructors for the sake of example): class MyDataChunk { //Look Ma! Implementation! }; class Sink; class Source { virtual void Run() = 0; Sink *next_; void SetNext(Sink *next) { next_ = next; } }; class Sink { virtual void GiveMeAChunk(const MyDataChunk& data) { //Impl }; }; class In { virtual void Run { //Impl } }; class Out { }; //Note how filter and sorter have the same declaration. Concrete classes //will inherit from them. The seperate names are there to ensure only //that some idiot doesn't go in and put in a filter where someone expects //a sorter, etc. class Filter : public Source, public Sink { //Drop objects from the chain-of-command pattern that don't match a particular //criterion. }; class Sorter : public Source, public Sink { //Sorts inputs to outputs. There are different sorters because someone might //want to sort by filename, size, date, etc... }; class MyClass { In i; Out o; Filter f; Sorter s; public: //Functions to set i, o, f, and s void Execute() { i.SetNext(f); f.SetNext(s); s.SetNext(o); i.Run(); } }; What I don't want is for somebody to come back later and go, "Hey, look! Sorter and Filter have the same signature. I can make a common one that does both!", thus breaking the semantic difference MyClass requires. Is this a common kind of requirement, and if so, how might I implement a test for it?

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  • Why is this statement treated as a string instead of its result?

    - by reve_etrange
    I am trying to perform some composition-based filtering on a large collection of strings (protein sequences). I wrote a group of three subroutines in order to take care of it, but I'm running into trouble in two ways - one minor, one major. The minor trouble is that when I use List::MoreUtils 'pairwise' I get warnings about using $a and $b only once and them being uninitialized. But I believe I'm calling this method properly (based on CPAN's entry for it and some examples from the web). The major trouble is an error "Can't use string ("17/32") as HASH ref while "strict refs" in use..." It seems like this can only happen if the foreach loop in &comp is giving the hash values as a string instead of evaluating the division operation. I'm sure I've made a rookie mistake, but can't find the answer on the web. The first time I even looked at perl code was last Wednesday... use List::Util; use List::MoreUtils; my @alphabet = ( 'A', 'R', 'N', 'D', 'C', 'Q', 'E', 'G', 'H', 'I', 'L', 'K', 'M', 'F', 'P', 'S', 'T', 'W', 'Y', 'V' ); my $gapchr = '-'; # Takes a sequence and returns letter = occurrence count pairs as hash. sub getcounts { my %counts = (); foreach my $chr (@alphabet) { $counts{$chr} = ( $[0] =~ tr/$chr/$chr/ ); } $counts{'gap'} = ( $[0] =~ tr/$gapchr/$gapchr/ ); return %counts; } # Takes a sequence and returns letter = fractional composition pairs as a hash. sub comp { my %comp = getcounts( $[0] ); foreach my $chr (@alphabet) { $comp{$chr} = $comp{$chr} / ( length( $[0] ) - $comp{'gap'} ); } return %comp; } # Takes two sequences and returns a measure of the composition difference between them, as a scalar. # Originally all on one line but it was unreadable. sub dcomp { my @dcomp = pairwise { $a - $b } @{ values( %{ comp( $[0] ) } ) }, @{ values( %{ comp( $[1] ) } ) }; @dcomp = apply { $_ ** 2 } @dcomp; my $dcomp = sqrt( sum( 0, @dcomp ) ) / 20; return $dcomp; } Much appreciation for any answers or advice!

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  • Can I have a CASE statement within a WHILE loop?

    - by John
    This is what I'm doing: while (@counter < 3 and @newBalance >0) begin CASE when @counter = 1 then ( @monFee1 = @monthlyFee, @newBalance = @newBalance-@fee) when @counter = 2 then ( @monFee2 = @monthlyFee, @newBalance = @newBalance-@fee) END @counter = @counter +1 end I get this error: Incorrect syntax near the keyword 'CASE'. No idea why. Please help!

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  • please check my MYSQL query & give me advice?

    - by Suba
    select s.s_nric as NRIC,s.s_name as NAME,s.s_psle_eng as PSLE_ENG,s.s_psle_math as PSLE_MATHS,s.s_psle_aggr as PSLE_AGGR, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEEN%' AND re.re_year='2008' AND re.re_semester='2' AND re.re_nric=s.s_nric ) as English_2008, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEMA%' AND re.re_year='2008' AND re.re_semester='2' AND re.re_nric=s.s_nric ) Maths_2008, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEEN%' AND re.re_year='2009' AND re.re_semester='2' AND re.re_nric=s.s_nric ) as English_2009, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEMA%' AND re.re_year='2009' AND re.re_semester='2' AND re.re_nric=s.s_nric ) Maths_2009 ,isc.isc_g_gpa as ISC_GPA from si_student_data as s LEFT JOIN si_isc_gpa as isc ON isc.isc_g_nric=s.s_nric where 1=1 AND s.s_admission_year='2008' GROUP BY s.s_nric ORDER BY s.s_gender,s.s_name asc This is my query. please check my sub query this is my sub query (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEEN%' AND re.re_year='2008' AND re.re_semester='2' AND re.re_nric=s.s_nric ) as English_2008, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEMA%' AND re.re_year='2008' AND re.re_semester='2' AND re.re_nric=s.s_nric ) Maths_2008, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEEN%' AND re.re_year='2009' AND re.re_semester='2' AND re.re_nric=s.s_nric ) as English_2009, (SELECT re.re_mark FROM si_results re WHERE re.re_code like 'FEMA%' AND re.re_year='2009' AND re.re_semester='2' AND re.re_nric=s.s_nric ) Maths_2009 When I execute my query, server take long time to execute. So how to make simple? please advice me. Thanks.

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  • How can I evaluate a deferred Linq statement when debugging?

    - by DanO
    I'm debugging in VS2010, and I want to inspect a string value but all I can get the debugger to show me (through watches, hovering, locals, etc.) is: "System.Linq.Enumerable+<TakeIterator>d__3a`1[System.Char]" I don't care if there are side effects from premature evaluation or whatever, I just want to see what the expression would evaluate to if I evaluate it right now at the current breakpoint. How is this done? Also can I change my code in such a way that it evaluates earlier? Not that I care when I'm not debugging... but just wondering. In case it is relevant... (I doubt it.) I'm stuffing a new entity object before saving it to the database... some fields are assigned with LINQ statements, I'm not sure when they get evaluated under the covers of EF. The DB update fails with 'string or binary data would be truncated... So I'm trying to find the too-long field.

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  • Is it possible to refactor this C# if(..) statement?

    - by Pure.Krome
    Hi folks, simple question :- i have the following simple if (..) statements :- if (foo == Animal.Cat || foo == Animal.Dog) { .. } if (baa == 1|| baa == 69) { .. } is it possible to refactor these into something like ... DISCLAIMER: I know this doesn't compile .. but this is sorta what i'm trying to get... if (foo == (Animal.Cat || Animal.Dog)) { .. } if (baa == (1 || 69)) { .. } Cheers :) EDIT I wonder if a lambda expression extension could do this? :P

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  • jQuery Ajax loads URL multiple times, how do I unbind/rebind properly?

    - by gmoz22
    I load a SELECT element via Ajax (list of brands), get its selected value (brand id) and load another SELECT via another Ajax URL (list of templates for currently selected brand). Here's my code: $(document).ready( function() { // DO NOT cache Ajax calls $.ajaxSetup ({ cache: false }); // loader var ajax_load = "Loading..."; // Brands List URL var loadBrandUrl = "getBrandsList.php"; // Templates List URL var loadTemplateUrl = "getTemplatesList.php"; $("#brandslistSelect").html(ajax_load).load(loadBrandUrl) .ajaxComplete(function(){ // Brands select loaded /* Load Templates SELECT the first time since no .change() has happened */ var selectedBrand = $("#brandslistSelect option:selected").attr("value"); // get the value console.log(selectedBrand); // Log selected brand to console // get Templates select, commented for now since it does an infinite loop // $("#templateslistSelect").html(ajax_load).load(loadTemplateUrl, { BrandId: selectedBrand } ); /* End initial load template */ /* On interaction with the Brands SELECT */ $("#brandslistSelect").change(function () { // on interaction with select selectedBrand = $("#brandslistSelect option:selected").attr("value"); // get the value // get Templates SELECT $("#templateslistSelect").html(ajax_load).load(loadTemplateUrl, { BrandId: selectedBrand } ) }); /* End interaction with the Brands SELECT */ }); }); It returns selectedBrand in the console 3 times : selectedBrand = undefined selectedBrand = undefined selectedBrand = 101 Now, if I uncomment the following line, same output as above but it also loads the templates URL indefinitely : // $("#templateslistSelect").html(ajax_load).load(loadTemplateUrl, { BrandId: selectedBrand } ); Any idea how I could modify this code to make it work as intended? Thanks for your help stackOverflow community!

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  • How do make dependency generation work for C? (Also..decode this sed/make statement!)

    - by Derek
    Hi all. I have a make build system that I am trying to decipher that someone else wrote. I am getting an error when I run it on a redhat system, but not when I run it on my solaris system. The versions of gmake are the same major revision (one off on minor revision). This is for building a C project, and the make system has a global Makefile.global that is inherited by each directory's local Makefile The Makefile.global has all the targets in it, starting with all: $(LIB) $(BIN) where LIB builds libs and BIN builds binaries. jumping down the targets I have $(LIB) : $(GEN_LIB) $(GEN_LIB) : $(GEN_DEPS) $(GEN_OBJS) $(AR) $(ARFLAGS) $(GEN_LIB) $(GEN_OBJS) $(GEN_DEPS) : @set -e; rm -f $@; \ $(CC) $(CDEP_FLAG) $(CFLAGS) $(INCDIRS) `basename $@ | sed 's/\.d/\.c/' | sed 's,^,$(HOME_SRC)/,'` | sed 's,\(.*\)\.o: ,$(GEN_OBJDIR)/\1.o $@ :,g' > [email protected] ; \ cat [email protected] > $@ ; \ cat [email protected] | cut -d: -f2 | grep '\.h' | sed 's,\.h,.h :,g' >> $@ ; \ rm [email protected] $(GEN_OBJS) : $(CC) $(CFLAGS) $(INCDIRS) -c $(*F).c -lmpi -o $@ I think these are all the relevant targets I need to include to answer my question. Definitions of those variables: CC = icc CDEP_FLAG = -M CFLAGS = various compiler flags ifdef type flags INCDIRS = include directory where all .h files are GEN_OBJDIR = /lib/objs HOME_SRC = . GEN_LIB = lib/$(LIB) GEN_DEPDIR=/lib/deps GEN_DEPS = $(addprefix $(GEN_DEPDIR)/,$(addsuffix .d,$(basename $(OBJS)))) I think this has everything covered you need. Basically self explanatory from the names. Now as best I can tell, this is generating in /lib/deps a .d file that has the object and source dependencies in it. In other words, for the utilities.a library, I will get a utils.o and utils.c dependency stack, all in the file utils.d There is some syntax error that is being generated in that file I think, because I get the following error: ../lib/deps/util.d:25: *** target pattern contains no '%'. Stop. gmake[2]: *** [all] Error 2 gmake[1]: *** [all] Error 2 gmake: *** [all] Error 2 I am not sure if my error is in the dependency generation, or some further down part, like the object generation target? If you need further info, let me know, I will add to post

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  • How is this statement making sense? (Sun's naming convention for Java variables)

    - by polygenelubricants
    I've been quoting this segment from Sun's document for the past few days, and only now do I stop and think about what it's saying, and I can't make sense out of it. Please keep in mind that English is not my first language. Naming conventions Variables: Except for variables, all instance, class, and class constants are in mixed case with a lowercase first letter. How is this making sense? Isn't this saying that class names are in mixed case with a lowercase first letter? Like I should name it class myClass? And class constants are also in mixed case with a lowercase first letter? Like I should name it Integer.maxValue? And is it really saying anything about how variables themselves should be named? Am I not parsing this properly or is this actually a blatant error?

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  • Do you use logical negation operator (!) in "if" statement or check on "== false"

    - by Taras Terebkov
    Hello everyone, I just want to conduct a little survey about code style developers prefer. For me there are two ways to write "if" in such languages as Java, C#, C++, etc. (1) Logical negation operator public void foo() { if (!SessionManager.getInstance().hasActiveSession()) { . . . . . } } (2) Check on "false" public void foo() { if (SessionManager.getInstance().hasActiveSession() == false) { . . . . . } } I always believe that first way is much worst then the second one. Cause usually you don't "read" the code, but "recognize" it in one brief look. And exclamation symbol slipped from your mind, just disturbing you somewhere on the bottom of your unconscious. And only during reading the "if" block below you understand, that the logic is opposite - no sessions in "if" On the other hand in the second way of writing, an eye immediately catches words "SessionManager", "hasActiveSession" and "false". Also for me, the situation with "true" is different. In code like class SessionManager { private bool hasSession; public void foo() { if (hasSession == true) { . . . . . } else { . . . . . } } } I find "true" superfluous. why we repeating the sentence two times? The following is shorter and quicker to catch. class SessionManager { private bool hasSession; public void foo() { if (hasSession) { . . . . . } else { . . . . . } } } What do YOU think, guys?

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  • jQuery select image in div if image parent does't have a certain class.

    - by Alex
    Wordpress wraps images with captions in a div with a class of .wp-caption. I'm looking for a way to select images that don't have this div so I can wrap them in different div. (to keep a consistent border around all the images) <div class="blog-post-content"> <div id="attachment_220" class="wp-caption alignleft" style="width: 310px"> <a href="/somewhere/"><img class="size-medium wp-image-220" src="/path/to/image" alt="" width="300" height="280" /></a> <p class="wp-caption-text">Caption Text</p> </div> <p>This is the body of the post</p> </div> To test my selector, I'm just trying to add a green border. I can handle the .wrap() once the selector is working. The most promising of my attempts is: $('.blog-post-content img').parent('div:not(".wp-caption")').css('border', '2px solid green'); ... but no luck.

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  • C++ include statement required if defining a map in a headerfile.

    - by Justin
    I was doing a project for computer course on programming concepts. This project was to be completed in C++ using Object Oriented designs we learned throughout the course. Anyhow, I have two files symboltable.h and symboltable.cpp. I want to use a map as the data structure so I define it in the private section of the header file. I #include <map> in the cpp file before I #include "symboltable.h". I get several errors from the compiler (MS VS 2008 Pro) when I go to debug/run the program the first of which is: Error 1 error C2146: syntax error : missing ';' before identifier 'table' c:\users\jsmith\documents\visual studio 2008\projects\project2\project2\symboltable.h 22 Project2 To fix this I had to #include <map> in the header file, which to me seems strange. Here are the relevant code files: // symboltable.h #include <map> class SymbolTable { public: SymbolTable() {} void insert(string variable, double value); double lookUp(string variable); void init(); // Added as part of the spec given in the conference area. private: map<string, double> table; // Our container for variables and their values. }; and // symboltable.cpp #include <map> #include <string> #include <iostream> using namespace std; #include "symboltable.h" void SymbolTable::insert(string variable, double value) { table[variable] = value; // Creates a new map entry, if variable name already exist it overwrites last value. } double SymbolTable::lookUp(string variable) { if(table.find(variable) == table.end()) // Search for the variable, find() returns a position, if thats the end then we didnt find it. throw exception("Error: Uninitialized variable"); else return table[variable]; } void SymbolTable::init() { table.clear(); // Clears the map, removes all elements. }

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  • SELECT product from subclass: How many queries do I need?

    - by Stefano
    I am building a database similar to the one described here where I have products of different type, each type with its own attributes. I report a short version for convenience product_type ============ product_type_id INT product_type_name VARCHAR product ======= product_id INT product_name VARCHAR product_type_id INT -> Foreign key to product_type.product_type_id ... (common attributes to all product) magazine ======== magazine_id INT title VARCHAR product_id INT -> Foreign key to product.product_id ... (magazine-specific attributes) web_site ======== web_site_id INT name VARCHAR product_id INT -> Foreign key to product.product_id ... (web-site specific attributes) This way I do not need to make a huge table with a column for each attribute of different product types (most of which will then be NULL) How do I SELECT a product by product.product_id and see all its attributes? Do I have to make a query first to know what type of product I am dealing with and then, through some logic, make another query to JOIN the right tables? Or is there a way to join everything together? (if, when I retrieve the information about a product_id there are a lot of NULL, it would be fine at this point). Thank you

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  • Why the valid looking statement gives error in MATLAB?

    - by user198729
    It's from this question? Why the two solutions doesn't work, though it looks very valid for me: >> t = -pi:0.1:pi; >> r = ((sin(t)*sqrt(cos(t)))*(sin(t) + (7/5))^(-1)) - 2*sin(t) + 2 ; ??? Error using ==> mtimes Inner matrix dimensions must agree. >> t = -pi:0.1:pi; >> r = ((sin(t).*sqrt(cos(t))).*(sin(t) + (7/5)).^(-1)) - 2*sin(t) + 2 ; >> plot(r,t) ??? Error using ==> plot Vectors must be the same lengths. What's wrong with the above?

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  • What's wrong with this UPDATE FROM using a case statement?

    - by Blankman
    update p set p.storePrice = CASE WHEN p.costPrice BETWEEN 0.00 AND 1.00 THEN p.costPrice * 1.0 CASE WHEN p.costPrice BETWEEN 0.00 AND 1.00 THEN p.costPrice * 1.0 ELSE p.msrpPrice END FROM product p WHERE p.type = 1 The error says: Msg 156, Level 15, State 1, Line 9 Incorrect syntax near the keyword 'CASE'. I can't seem to see any issue with the sql?

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  • How to make if-elif-else statement in python more space-saving?

    - by Neverland
    I have a lot of if-elif-else statements in my code if message == '0' or message == '3' or message == '5' or message == '7': ... elif message == '1' or message == '2' or message == '4' or message == '6' or message == '8': ... else: ... Is it possible to format this in a more space-saving way? I tried it this way: if message == '0' or '3' or '5' or '7': ... elif message == '1' or '2' or '4' or '6' or '8': ... else: ... But without success.

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  • scala 2.8.0.RC2 compiler problem on pattern matching statement?

    - by gruenewa
    Why does the following module not compile on Scala 2.8.RC[1,2]? object Test { import util.matching.Regex._ val pVoid = """\s*void\s*""".r val pVoidPtr = """\s*(const\s+)?void\s*\*\s*""".r val pCharPtr = """\s*(const\s+)GLchar\s*\*\s*""".r val pIntPtr = """\s*(const\s+)?GLint\s*\*\s*""".r val pUintPtr = """\s*(const\s+)?GLuint\s*\*\s*""".r val pFloatPtr = """\s*(const\s+)?GLfloat\s*\*\s*""".r val pDoublePtr = """\s*(const\s+)?GLdouble\s*\*\s*""".r val pShortPtr = """\s*(const\s+)?GLshort\s*\*\s*""".r val pUshortPtr = """\s*(const\s+)?GLushort\s*\*\s*""".r val pInt64Ptr = """\s*(const\s+)?GLint64\s*\*\s*""".r val pUint64Ptr = """\s*(const\s+)?GLuint64\s*\*\s*""".r def mapType(t: String): String = t.trim match { case pVoid() => "Unit" case pVoidPtr() => "ByteBuffer" case pCharPtr() => "CharBuffer" case pIntPtr() | pUintPtr() => "IntBuffer" case pFloatPtr() => "FloatBuffer" case pShortPtr() | pUshortPtr() => "ShortBuffer" case pDoublePtr() => "DoubleBuffer" case pInt64Ptr() | pUint64Ptr() => "LongBuffer" case x => x } }

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