On Friday, 24 February 2017 at 14:06:22 UTC, Meta wrote:
On Friday, 24 February 2017 at 11:17:46 UTC, John Colvin wrote:
Unfortunately that only works by accident of my example. A
counterexample:
T foo(Q = float, T = short)(T t) { return t; }
alias Typeof(alias v) = typeof(v);
template getInstantiation(alias f, T...)
{
import std.meta;
alias getInstantiation = f!(staticMap!(Typeof, T));
}
static assert(is(typeof(foo(3)) == int)); // ok
static assert(is(typeof(getInstantiation!(foo, 3)(3)) ==
int)); // fails
This looks like VRP is kicking in when it shouldn't, or maybe
it's a different bug. 3 should be typed as int by default
unless we explicitly ask for something else.
VRP propagation is what makes the call possible, but that's a
distraction. The problem is that getInstantiation is setting Q to
int and leaving T to be it's default type of short, which is not
the same as if you just call with an int (which infers T from t
and leaves Q as it's default float. Fundamentally, you can't
assume the same order of runtime and template arguments.
