Re: template parameter inference and introspection

[Meta via Digitalmars-d-learn]

On Thursday, 23 February 2017 at 18:21:51 UTC, Meta wrote:
On Thursday, 23 February 2017 at 16:01:44 UTC, John Colvin 
wrote:
Is there any way to get a reference/alias to the instantiation 
of a template function that would be called, given certain 
parameters? I.e. to get the result of whatever template 
parameter inference (and overload resolution) has occurred?

E.g. for some arbitrarily complex foo:

static assert(__traits(compiles, foo(3)));
alias fooWithInt = someMagic(foo(3));

so if foo was `void foo(T)(T t) {}` then `fooWithInt` would be 
`foo!int`, but if it was `void foo(Q = float, T = long)(T t)` 
then `fooWithInt` would be `foo!(float, int)`

I don't believe so, because foo(3) is a value (void), not a 
type like foo!int would be. You can't get it back after you've 
called the function. You would have to do something like:

alias fooWithInt = someMagic!foo(3);

Where someMagic constructs the alias to foo!int based on the 
type of arguments passed, or something like that.

A quick and rough example I threw together. Annoyingly, I can't 
figure out a way to tell the compiler that I want to printout the 
symbol of fooWithInt, not call it without parens. The best I can 
do is print out its type.

void foo(T)(T t) {}
void foo(Q = float, T = long)(T t) {}

alias Typeof(alias v) = typeof(v);

template getInstantiation(alias f, T...)
{
    import std.meta;

    alias getInstantiation = f!(staticMap!(Typeof, T));
}

alias fooWithInt = getInstantiation!(foo, 3);
alias fooWithLong = getInstantiation!(foo, 3L);

void main()
{
    pragma(msg, typeof(fooWithInt));
    pragma(msg, typeof(fooWithLong));
}