trusted purity?

[Kenji Hara]

Hmm. Interesting approach. I tried to utilize the "trusted pure" concept .

template TrustedPure(alias func)
{
    import std.traits, std.algorithm;

    alias F1 = FunctionTypeOf!(func);
    static if (functionAttributes!F1 & FunctionAttribute.pure_)
    {
        alias TrustedPure = func;
    }
    else
    {
        alias F2 = SetFunctionAttributes!(
            F1,
            functionLinkage!F1,
            functionAttributes!F1 | FunctionAttribute.pure_);

        auto ref TrustedPure(A...)(auto ref A args)
        pure    // mark as expected
        @system // represent 'unsafe' operation.
        {
            // forward!args does not work, because
            // std.algorithm.move is not pure...
            return (cast(F2*)&func)(/*forward!*/args);
        }
    }
}
void main() pure
// cannot add @safe, because TrustedPure functions are always @system
{
    import core.stdc.stdlib;
    alias pmalloc = TrustedPure!(core.stdc.stdlib.malloc);
    alias pfree = TrustedPure!(core.stdc.stdlib.free);

    auto p = cast(int*)pmalloc(int.sizeof);
    *p = 100;
    pfree(p);
}

Kenji Hara


2013/4/30 monarch_dodra <monarchdodra at gmail.com>

> I'm getting strange behavior trying to cast to pure. This is my
> test program:
>
> //--------
> import std.stdio;
> import core.stdc.stdlib;
>
> void main()
> {
>      auto p1 = &core.stdc.stdlib.free;
>      auto p2 = cast(void function(void*))&core.stdc.**stdlib.free;
>      auto p3 = cast(void function(void*)
> pure)&core.stdc.stdlib.free;
>      auto pp1 = core.stdc.stdlib.malloc(5);
>      auto pp2 = core.stdc.stdlib.malloc(5);
>      auto pp3 = core.stdc.stdlib.malloc(5);
>      writeln(p1);
>      p1(pp1);
>      writeln(p2);
>      p2(pp2); //This hangs
>      writeln(p3); //Never reaches here
>      p3(pp3);
> }
> //--------
>
> Am I doing something wrong? Could somebody else test this? I'm on
> win32.
>
> I've also been getting some object violations trying to use this
> cast...
>
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