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• The purpose of using a constants pool for immutable constants

  - by patstuart

  Originally posted at stackoverflow.com/q/23961260 I come across the following code with a lot of frequency: if (myArray.length == Constants.ZERO_INT) or if (myString != null && !myString.equals(Constants.EMPTY_STRING)) Neither of these makes much sense to me. Isn't the point of having a constant pool for ease of code appearance and to allow for modularity? In both of the above cases, it just looks like needless noise that accomplishes neither objective. My question: what is the purpose of using a constants pool for variables like this which will never change? Or is this just cargo cult programming? If so, then why does it seem to be prevalent in the industry? (I've noticed it with at least two different employers I've worked with).

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• Delphi: All constants are constant, but some are more constant than others?

  - by Ian Boyd

  Consider: clHotlight: TColor = $00FF9933; clLink = clHotLight; //alias of clHotlight [Error] file.pas: Constant expression expected and the alternate wording that works: clHotlight = TColor($00FF9933); clLink = clHotLight; //alias of clHotlight Explain. Then consider: AdministratorGUID: TGUID = '{DE44EEA0-6712-11D4-ADD4-0006295717DA}'; SuperuserGUID = AdministratorGUID; //alias of AdministratorGUID [Error] file.pas: Constant expression expected And fix.

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• Using nested classes for constants?

  - by antirysm

  What's wrong with using nested classes to group constants? Like so: public static class Constants { public static class CategoryA { public const string ValueX = "CatA_X"; public const string ValueY = "CatA_Y"; } public static class CategoryB { public const string ValueX = "CatB_X"; public const string ValueY = "CatB_Y"; } } Used like so: Console.WriteLine(Constants.CategoryA.ValueY); Console.WriteLine(Constants.CategoryB.ValueX); You could also make the "Constants"-class partial...

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• Write a compiler for a language that looks ahead and multiple files?

  - by acidzombie24

  In my language I can use a class variable in my method when the definition appears below the method. It can also call methods below my method and etc. There are no 'headers'. Take this C# example. class A { public void callMethods() { print(); B b; b.notYetSeen(); public void print() { Console.Write("v = {0}", v); } int v=9; } class B { public void notYetSeen() { Console.Write("notYetSeen()\n"); } } How should I compile that? what i was thinking is: pass1: convert everything to an AST pass2: go through all classes and build a list of define classes/variable/etc pass3: go through code and check if there's any errors such as undefined variable, wrong use etc and create my output But it seems like for this to work I have to do pass 1 and 2 for ALL files before doing pass3. Also it feels like a lot of work to do until I find a syntax error (other than the obvious that can be done at parse time such as forgetting to close a brace or writing 0xLETTERS instead of a hex value). My gut says there is some other way. Note: I am using bison/flex to generate my compiler.

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• How to write a very basic compiler [closed]

  - by Ali

  Possible Duplicate: Best Online resources to learn about Compilers? What would be the best way to learn about compilers, and executable formats? Advanced compilers like gcc compile codes into machine readable files according to the language in which the code has been written (e.g. C, C++, etc). In fact, they interpret the meaning of each codes according to library and functions of the corresponding languages. Correct me if I'm wrong. I wish to better understand compilers by writing a very basic compiler (probably in C) to compile a static file (e.g. Hello World in a text file). I tried some tutorials and books, but all of them are for practical cases. They deal with compiling dynamic codes with meanings connected with the corresponding language. How can I write a basic compiler to convert a static text into a machine readable file? The next step will be introducing variables into the compiler; imagine that we want to write a compiler which compile only some functions of a language. Introducing practical tutorials and resources is highly appreciated :-)

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• Can compiler optimization introduce bugs ?

  - by ereOn

  Hi, Today I had a discussion with a friend of mine and we debated for a couple of hours about "compiler optimization". I defended the point that sometimes, a compiler optimization might introduce bugs or at least, undesired behavior. My friend totally disagreed, saying that "compiler are built by smart people and do smart things" and thus, can never go wrong. He didn't convinced my at all, but I have to admit I lack of real-life examples to strengthen my point. Who is right here ? If I am, do you have any real-life example where a compiler optimization produced a bug in the resulting software ? If I'm mistaking, should I stop programming and learn fishing instead ? Thank you !

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• will reading compiler construction increase my programming skills?

  - by nicky

  will reading compiler construction increase my programming skills?

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• Extreme Optimization –Mathematical Constants and Basic Functions

  - by JoshReuben

  Machine constants The MachineConstants class - contains constants for floating-point arithmetic because the CLS System.Single and Double floating-point types do not follow the standard conventions and are useless. machine constants for the Double type: machine precision: Epsilon , SqrtEpsilon CubeRootEpsilon largest possible value: MaxDouble , SqrtMaxDouble, LogMaxDouble smallest Double-precision floating point number that is greater than zero: MinDouble , SqrtMinDouble , LogMinDouble A similar set of constants is available for the Single Datatype  Mathematical Constants The Constants class contains static fields for many mathematical constants and common expressions involving small integers – if you are doing thousands of iterations, you wouldn't want to calculate OneOverSqrtTwoPi , Sqrt17 or Log17 !!! Fundamental constants E - The base for the natural logarithm, e (2.718...). EulersConstant - (0.577...). GoldenRatio - (1.618...). Pi - the ratio between the circumference and the diameter of a circle (3.1415...). Expressions involving fundamental constants: TwoPi, PiOverTwo, PiOverFour, LogTwoPi, PiSquared, SqrPi, SqrtTwoPi, OneOverSqrtPi, OneOverSqrtTwoPi Square roots of small integers: Sqrt2, Sqrt3, Sqrt5, Sqrt7, Sqrt17 Logarithms of small integers: Log2, Log3, Log10, Log17, InvLog10  Elementary Functions The IterativeAlgorithm<T> class in the Extreme.Mathematics namespace defines many elementary functions that are missing from System.Math. Hyperbolic Trig Functions: Cosh, Coth, Csch, Sinh, Sech, Tanh Inverse Hyperbolic Trig Functions: Acosh, Acoth, Acsch, Asinh, Asech, Atanh Exponential, Logarithmic and Miscellaneous Functions: ExpMinus1 - The exponential function minus one, ex-1. Hypot - The hypotenuse of a right-angled triangle with specified sides. LambertW - Lambert's W function, the (real) solution W of x=WeW. Log1PlusX - The natural logarithm of 1+x. Pow - A number raised to an integer power.

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• Java best practice Interface - subclasses and constants

  - by Taiko

  In the case where a couple of classes implements an interface, and those classes have a couple of constants in common (but no functions), were should I put this constant ? I've had this problem a couple of times. I have this interface : DataFromSensors that I use to hide the implementations of several sub classes like DataFromHeartRateMonitor DataFromGps etc... For some reason, those classes uses the same constants. And there's nowere else in the code were it is used. My question is, were should I put those constants ? Not in the interface, because it has nothing to do with my API Not in a static Constants class, because I'm trying to avoid those Not in a common abstract class, that would stand between the interface and the subclasses, because I have no functions in common, only a couple of constants (TIMEOUT_DURATION, UUID, those kind of things) I've read best practice for constants and interface to define constants but they don't really answer my question. Thanks !

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• Learning to implement dynamic language compiler

  - by TriArc

  I'm interested in learning how to create a compiler for a dynamic language. Most compiler books, college courses and articles/tutorials I've come across are specifically for statically typed languages. I've thought of a few ways to do it, but I'd like to know how it's usually done. I know type inferencing is a pretty common strategy, but what about others? Where can I find out more about how to create a dynamically typed language?

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• Learning to implement dynamically typed language compiler

  - by TriArc

  I'm interested in learning how to create a compiler for a dynamically typed language. Most compiler books, college courses and articles/tutorials I've come across are specifically for statically typed languages. I've thought of a few ways to do it, but I'd like to know how it's usually done. I know type inferencing is a pretty common strategy, but what about others? Where can I find out more about how to create a dynamically typed language? Edit 1: I meant dynamically typed. Sorry about the confusion. I've written toy compilers for statically typed languages and written some interpreters for dynamically typed languages. Now, I'm interested in learning more about creating compilers for a dynamically typed language. I'm specifically experimenting with LLVM and since I need to specify the type of every method and argument, I'm thinking of ways to implement a dynamically typed language on something like LLVM.

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• Namespace constants and use as

  - by GordonM

  I'm having some problems with using constants from a namespace. If I define the constant and try to use as it, PHP seems unable to find it. For example, in my file with the constants I have code along the lines of the following: namespace \my\namespace\for\constants; const DS = DIRECTORY_SEPARATOR; Then in the consuming file I have: namespace \some\other\namespace; use \my\namespace\for\constants\DS as DS; echo (realpath (DS . 'usr' . DS 'local')); However, instead of echoing '/usr/local' as expected I get the following notice and an empty string. Notice: Use of undefined constant DS - assumed 'DS' If I change the code as follows: use \my\namespace\for\constants as cns; echo (realpath (cns\DS . 'usr' . cns\DS 'local')); I get the expected result, but it's obviously quite a bit less convenient than just being able to pull the constants in directly. You can alias a class/interface/trait in a namespace, are you not able to alias a constant too? If you can do it, then how?

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• Compiler warning when passing NSError ** as a method parameter

  - by splicer

  I've been scratching my head about this for the last 4 hours, trying out all kinds of little experiments, but I can't seem to figure out what's going wrong. Could this be a compiler bug? Test.m: - (id)initWithContentsOfURL:(NSURL *)aURL error:(NSError **)error { if (!(self = [super init])) { return nil; } return self; } main.m: NSError *error; Test *t = [[Test alloc] initWithContentsOfURL:[NSURL fileURLWithPath:@"/"] error:&error]; Here's the compiler warning (from main.m): warning: incompatible Objective-C types 'struct NSError **', expected 'struct NSDictionary **' when passing argument 2 of 'initWithContentsOfURL:error:' from distinct Objective-C type I'm using the latest versions of Xcode and Snow Leopard.

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• Can I get a C++ Compiler to instantiate objects at compile time

  - by gam3

  I am writing some code that has a very large number of reasonably simple objects and I would like them the be created at compile time. I would think that a compiler would be able to do this, but I have not been able to figure out how. In C I could do the the following: #include <stdio.h> typedef struct data_s { int a; int b; char *c; } info; info list[] = { 1, 2, "a", 3, 4, "b", }; main() { int i; for (i = 0; i < sizeof(list)/sizeof(*list); i++) { printf("%d %s\n", i, list[i].c); } } Using #C++* each object has it constructor called rather than just being layed out in memory. #include <iostream> using std::cout; using std::endl; class Info { const int a; const int b; const char *c; public: Info(const int, const int, const char *); const int get_a() { return a; }; const int get_b() { return b; }; const char *get_c() const { return c; }; }; Info::Info(const int a, const int b, const char *c) : a(a), b(b), c(c) {}; Info list[] = { Info(1, 2, "a"), Info(3, 4, "b"), }; main() { for (int i = 0; i < sizeof(list)/sizeof(*list); i++) { cout << i << " " << list[i].get_c() << endl; } } I just don't see what information is not available for the compiler to completely instantiate these objects at compile time, so I assume I am missing something.

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• How does a compiler initially compile itself?

  - by jdk

  I recently read the Mono C# compiler is able to compile itself. Cool. In the past I've heard of other languages doing the same. It twists my mind - seems like a chicken and egg problem. What comes first, second and third, etc?...

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• Sharing constants across a WCF service

  - by Sandor Davidhazi

  I have certain strings which contain special characters so they can not be shared as enum members across a WCF service. (Actually, they are keys for configuration values.) I want to be able to pass in the keys at client side and get back the config values. If there is a change, I only want to change the config keys at one place. Constants would be ideal, because they can be changed as strong references across the entire solution, and the underlaying value could be updated with a service reference update. Currently I can think of two possible solutions: Create a shared assembly and place the constants there Share the constants across the service. The problem is, I can't get the datacontractserializer to serialize the constants. Is that possible at all? Is the shared assembly the only option I have?

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• How to manage Constants in Application

  - by changed

  what is the best way to use Application Constants ? What i usually do is create a separate table in database of constants and reference them as foreign key in other table. In Java i use enum. But how to keep a single place of authority for constants in application and what are the different ways i can do that(like table or enum).

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• C# compiler error CS0006: metadata file is not found

  - by Rob

  I've built a c# compiler using the tutorial on MSDN and a few other resources including here, and I've gotten it to work until I add additional reference assemblies. My errors stem from adding "System.dll" and "System.Windows.Forms.dll" to the ReferenceAssemblies list. here's my code: private void SetUpCompilingParameters() { string ver = string.Format("{0}.{1}.{2}", Environment.Version.Major, Environment.Version.MajorRevision, Environment.Version.Build); string libDir = string.Format(@"{0}", Environment.CurrentDirectory); string raDir = @"C:\Program Files (x86)\Reference Assemblies\Microsoft\Framework\.NETFramework\v4.0"; string exWpfDir = string.Format(@"C:\WINDOWS\Microsoft.NET\Framework\v{0}\WPF", ver); string exDir = string.Format(@"C:\WINDOWS\Microsoft.NET\Framework\v{0}", ver); MyCompiler = new CSharpCodeProvider(); CompilingParam = new CompilerParameters(); CompilingParam.GenerateExecutable = false; CompilingParam.GenerateInMemory = true; CompilingParam.IncludeDebugInformation = false; CompilingParam.TreatWarningsAsErrors = false; CompilingParam.CompilerOptions = string.Format("/lib:{0}", libDir); CompilingParam.CompilerOptions = string.Format("/lib:{0}", raDir); CompilingParam.CompilerOptions = string.Format("/lib:{0}", exDir); //CompilingParam.CompilerOptions = string.Format("/lib:{0}", exWpfDir); CompilingParam.ReferencedAssemblies.Add("System.dll"); CompilingParam.ReferencedAssemblies.Add("System.Windows.Forms.dll"); } As you can see, I've explicitly referenced directories in CompilerOptions but its not helping. I'd like to test the solution on here on stackoverflow that utilizes: CompilingParam.ReferencedAssemblies.Add(typeof(System.Xml.Linq.Extensions).Assembly.Location); but I'm having trouble using it for the general System.dll etc...

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• Php error in closure compiler execution

  - by Mohammad

  When I run php-closure i get a PHP error Undefined index: HTTP_IF_NONE_MATCH in <b>/php-closure.php</b> on line <b>183</b> Line 184 of php-closure is trim($_SERVER['HTTP_IF_NONE_MATCH']) == $etag) { This error only happens when closure has already written the compressed javascript file to the directory once, if the directory is emptied the error does not appear. What does this error mean and how can I avoid it? Thank You So Much!

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• Where should you put constants and why?

  - by Tim Meyer

  In our mostly large applications, we usually have a only few locations for constants: One class for GUI and internal contstants (Tab Page titles, Group Box titles, calculation factors, enumerations) One class for database tables and columns (this part is generated code) plus readable names for them (manually assigned) One class for application messages (logging, message boxes etc) The constants are usually separated into different structs in those classes. In our C++ applications, the constants are only defined in the .h file and the values are assigned in the .cpp file. One of the advantages is that all strings etc are in one central place and everybody knows where to find them when something must be changed. This is especially something project managers seem to like as people come and go and this way everybody can change such trivial things without having to dig into the application's structure. Also, you can easily change the title of similar Group Boxes / Tab Pages etc at once. Another aspect is that you can just print that class and give it to a non-programmer who can check if the captions are intuitive, and if messages to the user are too detailed or too confusing etc. However, I see certain disadvantages: Every single class is tightly coupled to the constants classes Adding/Removing/Renaming/Moving a constant requires recompilation of at least 90% of the application (Note: Changing the value doesn't, at least for C++). In one of our C++ projects with 1500 classes, this means around 7 minutes of compilation time (using precompiled headers; without them it's around 50 minutes) plus around 10 minutes of linking against certain static libraries. Building a speed optimized release through the Visual Studio Compiler takes up to 3 hours. I don't know if the huge amount of class relations is the source but it might as well be. You get driven into temporarily hard-coding strings straight into code because you want to test something very quickly and don't want to wait 15 minutes just for that test (and probably every subsequent one). Everybody knows what happens to the "I will fix that later"-thoughts. Reusing a class in another project isn't always that easy (mainly due to other tight couplings, but the constants handling doesn't make it easier.) Where would you store constants like that? Also what arguments would you bring in order to convince your project manager that there are better concepts which also comply with the advantages listed above? Feel free to give a C++-specific or independent answer. PS: I know this question is kind of subjective but I honestly don't know of any better place than this site for this kind of question. Update on this project I have news on the compile time thing: Following Caleb's and gbjbaanb's posts, I split my constants file into several other files when I had time. I also eventually split my project into several libraries which was now possible much easier. Compiling this in release mode showed that the auto-generated file which contains the database definitions (table, column names and more - more than 8000 symbols) and builds up certain hashes caused the huge compile times in release mode. Deactivating MSVC's optimizer for the library which contains the DB constants now allowed us to reduce the total compile time of your Project (several applications) in release mode from up to 8 hours to less than one hour! We have yet to find out why MSVC has such a hard time optimizing these files, but for now this change relieves a lot of pressure as we no longer have to rely on nightly builds only. That fact - and other benefits, such as less tight coupling, better reuseability etc - also showed that spending time splitting up the "constants" wasn't such a bad idea after all ;-)

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• Constants by another name

  - by Dave DeLong

  First off, I've seen this question and understand why the following code doesn't work. That is not my question. I have a constant, which is declared like; //Constants.h extern NSString * const MyConstant; //Constants.m NSString * const MyConstant = @"MyConstant"; However, in certain contexts, it's more useful to have this constant have a much more descriptive name, like MyReallySpecificConstant. I was hoping to do: //SpecificConstants.h extern NSString * const MyReallySpecificConstant; //SpecificConstants.m #import "Constants.h" NSString * const MyReallySpecificConstant = MyConstant; Obviously I cannot do this (which is explained in the linked question above). My question is: How else (besides something like #define MyReallySpecificConstant MyConstant) can I provide a single constant under multiple names?

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• C Problem with Compiler?

  - by Solomon081

  I just started learning C, and wrote my hello world program: #include <stdio.h> main() { printf("Hello World"); return 0; } When I run the code, I get a really long error: Apple Mach-O Linker (id) Error Ld /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug/CProj normal x86_64 cd /Users/Solomon/Desktop/C/CProj setenv MACOSX_DEPLOYMENT_TARGET 10.7 /Developer/usr/bin/clang -arch x86_64 -isysroot /Developer/SDKs/MacOSX10.7.sdk -L/Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug -F/Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug -filelist /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/CProj.LinkFileList -mmacosx-version-min=10.7 -o /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Products/Debug/CProj ld: duplicate symbol _main in /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/helloworld.o and /Users/Solomon/Library/Developer/Xcode/DerivedData/CProj-cwosspupvengheeaapmkrhxbxjvk/Build/Intermediates/CProj.build/Debug/CProj.build/Objects-normal/x86_64/main.o for architecture x86_64 Command /Developer/usr/bin/clang failed with exit code 1 I am running xCode Should I reinstall DevTools?

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• What are the tools required to build a compiler?

  - by kevin

  What are the various tools that are required to build a compiler for a particular programming language, say C? I want to know how each part of the compiler works. So, I am trying to use all the existing tools like loader, linker, etc, and combine them together to build one compiler (or can just say "compiling a compiler"). Can any one list out all such tools that are required to build a fully functional one?

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• Variables versus constants versus associative arrays in PHP

  - by susmits

  I'm working on a small project, and need to implement internationalization support somehow. I am thinking along the lines of using constants to define a lot of symbols for text in one file, which could be included subsequently. However, I'm not sure if using variables is faster, or if I can get away with using associative arrays without too much of a performance hit. What's better for defining constant values in PHP, performance-wise -- constants defined using define("FOO", "..."), or simple variables like $foo = "...", or associative arrays like $symbols["FOO"]?

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• Using Constants in Perl

  - by David W.

  I am trying to define constants in Perl using the use Constant pragma: use Constant { FOO => "bar", BAR => "foo" }; I'm running into a bit of trouble, and hoping there's a standard way of handling it. First of all... I am defining a hook script for Subversion. To make things simple, I want to have a single file where the class (package) I'm using is in the same file as my actual script. Most of this package will have constants involved in it: print "This is my program"; package "MyClass"; use constant { FOO => "bar" }; sub new { yaddah, yaddah, yaddah. I would like my constant FOO to be accessible to my main program. I would like to do this without having to refer to it as MyClass::FOO. Normally, when the package is a separate file, I could do this in my main program: use MyClass qw(FOO); but, since my class and program are a single file, I can't do that. What would be the best way for my main program to be able to access my constants defined in my class? The second issue... I would like to use the constant values as hash keys: $myHash{FOO} = "bar"; The problem is that %myHash has the literal string FOO as the key and not the value of the constant. This causes problems when I do things like this: if (defined($myHash{FOO})) { print "Key " . FOO . " does exist!\n"; } I could force the context: if (defined("" . FOO . "")) { I could add parentheses: if (defined(FOO())) { Or, I could use a temporary variable: my $foo = FOO; if (defined($foo)) { None of these are really nice ways of handling this issue. So, what is the best way? Is there one way I'm missing? By the way, I don't want to use Readonly::Scalar because it is 1). slow, and 2). not part of the standard Perl package. I want to define my hook not to require additional Perl packages and to be as simple as possible to work.

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