[Issue 9608] Add introspection for templates

[d-bugmail at puremagic.com]

http://d.puremagic.com/issues/show_bug.cgi?id=9608



--- Comment #2 from Andrej Mitrovic <andrej.mitrovich at gmail.com> 2013-03-23 11:32:36 PDT ---
(In reply to comment #0)
> There would be a fair amount of design involved because currently there's no
> kind that expresses a template's parameters outside the template.

I don't think we need to design much. We could provide traits. For example:

    template A(alias sym)
    {
        __traits(getArity, sym);  // 2 - or paramCount
        __traits(isAliasParam, 0, sym);  // 0 == index of param
    }
    A!((a, b) => a.name < b.name);

    template B(alias sym)
    {
        __traits(isValueParam, 0, sym);  // true
        __traits(isTypeParam, 1, sym);  // true
        __traits(isVariadicParam, 2, sym);  // true
    }

    void X(int val, Type, Args...)(Args t) { return 0; }

    B!(X);

And then you could wrap all of this into a Phobos template which collects all
the data. let's call it TemplateInfo:

    template B(alias sym)
    {
        alias ti = TemplateInfo!sym;
        static assert(ti.params.count == 2);
        static assert(ti.params[0].isValueParam);
    }

    void X(Type, int val)() { }
    B!(X);

That sort of stuff.

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