http://d.puremagic.com/issues/show_bug.cgi?id=10875

           Summary: Introduce functionLinkageType to mirror
                    functionLinkage with an enum
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: Phobos
        AssignedTo: nobody@puremagic.com
        ReportedBy: andrej.mitrovich@gmail.com


--- Comment #0 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-08-23 04:51:27 PDT ---
Currently std.traits.functionLinkage returns the linkage type, but it returns it as a string. So if you have generic code, you might end up writing code like so:

-----
import std.traits;

extern(C) void func()
{
}

void main()
{
    enum linkage = functionLinkage!func;

    static if (linkage == "c")
    {
    }
    else
    static if (linkage == "D")
    {
    }
}
-----

Unfortunately there's a bug here, there is no lowercase "c" linkage type, only "C". It would be safer if functionLinkage returned an enum.

But since it's too late to change the return type, I propose we introduce an enum version:

-----
import std.traits;

extern(C) void func()
{
}

void main()
{
    // new trait which returns a LinkageType enum instance
    enum linkage = functionLinkageType!func;

    static if (linkage == LinkageType.c)
    {
    }
    else
    static if (linkage == LinkageType.d)
    {
    }
}
-----

This will also allow a user to generate code by using EnumMembers on the LinkageType enum.

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--- Comment #1 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-08-23 04:54:39 PDT ---
(In reply to comment #0)
> But since it's too late to change the return type, I propose we introduce an enum version:

Actually a reasonable alternative is to simply introduce the LinkageType enum which will have a string as its base type, so it can be used with the functionLinkage function:

enum LinkageType : string
{
    D = "D",
    C = "C",
    Windows = "Windows",
    Pascal = "Pascal",
    Cpp = "C++"
}

-----
import std.traits;

extern(C) void func()
{
}

void main()
{
    enum linkage = functionLinkage!func;

    static if (linkage == LinkageType.C)
    {
    }
    else
    static if (linkage == LinkageType.D)
    {
    }
}
-----

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bearophile_hugs@eml.cc changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bearophile_hugs@eml.cc


--- Comment #2 from bearophile_hugs@eml.cc 2013-08-23 06:25:57 PDT ---
(In reply to comment #1)

> Actually a reasonable alternative is to simply introduce the LinkageType enum which will have a string as its base type,

This is a nice idea to fix the original design mistake of using strings. Do you know of other functions/templates in Phobos that could enjoy this the same improvement?

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--- Comment #3 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-08-23 09:22:04 PDT ---
(In reply to comment #2)
> (In reply to comment #1)
> 
> > Actually a reasonable alternative is to simply introduce the LinkageType enum which will have a string as its base type,
> 
> This is a nice idea to fix the original design mistake of using strings. Do you know of other functions/templates in Phobos that could enjoy this the same improvement?

Nothing of the top of my head, but I think there are a few more.

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Andrej Mitrovic <andrej.mitrovich@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |pull
         AssignedTo|nobody@puremagic.com        |andrej.mitrovich@gmail.com


--- Comment #4 from Andrej Mitrovic <andrej.mitrovich@gmail.com> 2013-09-18 18:27:04 PDT ---
https://github.com/D-Programming-Language/phobos/pull/1587

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