On Tuesday, 2 February 2016 at 13:20:33 UTC, Voitech wrote:
Hi, Is it possible to bound T... in template with some type ?
For single Parameter declaration it can be done by T:SomeType
but variadics does not seems to have that possibility ?
Cheers
Two possible solutions... If you don't need to know the number of
arguments at compile time, you can use normal variadic arguments:
void test(T)(T[] args...) {
import std.stdio;
writeln(T.stringof);
}
class A { }
class B : A { }
class C : A { }
void main()
{
test(1,2,3); // int
test(4,5,6.9); // double
static assert(!__traits(compiles, test(1,"xyz",9)));
// unfortunately, this doesn't work either:
//test(new B(), new C());
}
The last call should work IMO, but it doesn't. I believe that's a
compiler bug.
The other solution is to use `CommonType` as a template
constraint:
import std.traits;
void test(T...)(T args)
if(!is(CommonType!T == void))
{
import std.stdio;
writeln(T.stringof);
}
class A { }
class B : A { }
class C : A { }
void main()
{
test(1,2,3); // (int, int, int)
test(4,5,6.9); // (int, int, double)
static assert(!__traits(compiles, test(1,"xyz",9)));
test(new B(), new C()); // (B, C)
}
As you can see, here the types don't need to match exactly, but
they need to have a common base type.
