On 04/10/2011 04:10 PM, spir wrote:
Hello,
I need a trick to allow a function template parameter be optional.
The following (reduced case) fails because D wants to call f:
uint f(uint i) { return i; }
struct S (alias func=null) {
enum bool hasFunc = !(func == null); // *** error line ***
}
unittest {
// ok
auto s1 = S!()();
writeln(s1.hasFunc);
// not ok
auto s2 = S!(f)();
writeln(s2.hasFunc);
}
==>
Error: function ___.f (uint i) is not callable using argument types ()
(I consider that a bug due to "f" implicitely meaning "f()" --but this is
another story.)
Found one solution using isCallable! Other tricks welcome...
uint f(uint i) { return i; }
struct S (alias func=null) {
enum bool hasFunc = isCallable!(typeof(func));
}
unittest {
auto s1 = S!()();
writeln(s1.hasFunc);
auto s2 = S!(f)();
writeln(s2.hasFunc);
}
I'd also like to know why pointer cannot be template *alias* parameters, like
in:
auto s2 = S!(&f)();
==>
Error: expression & f is not a valid template value argument
Denis
--
_________________
vita es estrany
spir.wikidot.com
