http://d.puremagic.com/issues/show_bug.cgi?id=6207

           Summary: Mixin template evaluated to string can convert to
                    string mixin expression implicitly
           Product: D
           Version: D2
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: enhancement
          Priority: P2
         Component: DMD
        AssignedTo: nobody@puremagic.com
        ReportedBy: k.hara.pg@gmail.com


--- Comment #0 from Kenji Hara <k.hara.pg@gmail.com> 2011-06-24 03:48:28 PDT ---
If mixin template instantiation makes manifest constant string and it appears in expression context, the compiler converts it implicitly to string mixin expression.

This enhancement feature does not conflict with any existing features. Because normal instantiating with mixin template is illegal.

Sample code:
----
mixin template expand(string code)
{
    static if (code.length >= 2 && code[0..2] == "$x")
    {
        enum expand = `x` ~ code[2..$];
        pragma(msg, expand);
    }
    else
        enum expand = code;
}

void main()
{
    int x = 1;
    int y = expand!q{$x+2};
        // Rhs is implicitly converted to mixin(expand!(q{$x+2}))
    assert(y == 3);
}
----

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--- Comment #1 from Kenji Hara <k.hara.pg@gmail.com> 2011-10-16 18:58:34 PDT ---
We can improve the string lambda features in std.algorithm!

mixin template map(string pred)
{
    enum map = `map!((a){ return `~pred~`; })`;
}
template map(alias pred)
{
    auto map(E)(E[] r)
    {
        E[] result;
        foreach (e; r)
            result ~= pred(e);
        return result;
    }
}

void main()
{
    int b = 10;
    auto r = map!q{ a * b }([1,2,3]);
    //   --> mixin(`map!((a){ return ` ~ q{ a * b } ~ `; })`)([1,2,3])
    //   --> map!((a){ return  a * b ; })([1,2,3]);
    assert(r == [10,20,30]);
}

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Kenji Hara <k.hara.pg@gmail.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |patch


--- Comment #2 from Kenji Hara <k.hara.pg@gmail.com> 2011-10-16 20:21:17 PDT ---
https://github.com/D-Programming-Language/dmd/pull/459

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Walter Bright <bugzilla@digitalmars.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bugzilla@digitalmars.com


--- Comment #3 from Walter Bright <bugzilla@digitalmars.com> 2012-11-19 20:30:10 PST ---
See the pull request for more discussion.

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