Re: How to check for instantiation of specific template?

[Jacob Carlborg]

On 2013-10-10 19:23, H. S. Teoh wrote:

I have a template used for storing compile-time values:

        template Def(int x, string y) {
                alias impl = TypeTuple!(x,y);
        }

How do I define a template isDef that, given some template alias A,
evaluates to true if A is some instantiation of Def?

        template isDef(alias A) {
                enum A = ... /* what to put here? */
        }

The intent is to be able to write signature constraints like this:

        auto myFunc(alias def)(...)
                if (isDef!def)
        {
                ...
        }

        ...
        // Pass an instantiation of Def to myFunc
        auto x = myFunc!(Def!(1, "abc"))(args);

I tried using std.traits.isInstanceOf but apparently it expects the
second argument to be an actual type, which doesn't work in this case
because Def is a typetuple of compile-time values, not an actual type.

I found this old thread

http://forum.dlang.org/thread/mailman.1382.1371938670.13711.digitalmar...@puremagic.com

With this code:

template getTemplate(alias T : TI!TP, alias TI, TP...)
{
    alias getTemplate = TI;
}

But I haven't figured out how to do the comparison.

--
/Jacob Carlborg