On Thursday, 7 April 2016 at 21:36:37 UTC, Alex Parrill wrote:
On Thursday, 7 April 2016 at 20:31:12 UTC, jmh530 wrote:
I've been playing around with __traits and I find myself
confused on one aspect. In the code below, I was testing
whether some templates would compile given types. For the most
part it works as I would expect.
[...]
Neither the third nor sixth lines should be true.
alias wrongfoo = foo!int; /* Error: template instance
foo!int does not match template declaration foo(T, U)(T x, U y)
if (isNumeric!T && isNumeric!U) */
alias rightfoo = foo!(int, int); /* ok */
File a DMD bug.
(Also, you can use static assert here to check the assertions
at build-time instead of run-time)
is(typeof()) gives the expected results:
import std.traits : isNumeric;
import std.range : isInputRange;
void foo(T, U)(T x, U y) if (isNumeric!T && isNumeric!U) { }
void bar(T, U)(T x, U y) if (isNumeric!T && isInputRange!U) { }
unittest
{
static assert(is(typeof(foo!(int, int)))); //I get this
static assert(!is(typeof(foo!(bool, bool)))); //I get this
static assert(!is(typeof(foo!(int)))); //I think I get this
static assert(is(typeof(bar!(int, int[])))); //I get this
static assert(!is(typeof(bar!(int, int)))); //I get this
static assert(!is(typeof(bar!(int)))); //I don't get this
}
(note well I have changed the assertion 3 and 6).
There must be a subtle difference between __traits(compile,...)
and is(typeof()).
Does "compiles" mean that you've get something but that this
thing is not always of a valid type ?
