On Tuesday, 12 March 2013 at 14:24:11 UTC, TommiT wrote:
The difference is in function overload resolution. Polymorphic
concept based template would know about the hierarchical nature
of the concepts, say ForwardRange is a sub-concept of
InputRange, and thus the function overload resolution would be
able to choose the template which has the most
derived/specialized concept parameter that still matches with
the given template argument.
Example:
void foo(R)(R) if (isInputRange!R) { }
void foo(R)(R) if (isForwardRange!R) { }
int[] arr;
foo(arr); // ambiguity error
// Polymorphic concept to the rescue:
concept InputRange {
// definition of the concept
...
}
// ForwardRange is an extension of InputRange
concept ForwardRange : InputRange {
...
}
void bar(InputRange R)(R) { }
void bar(ForwardRange R)(R) { }
int[] arr;
bar(arr); // calls the second one
