Even then this "hides" some errors and debugging isn't easy
(figuring out why the template constraint failed). I've been
planning on creating a DIP addressing this for ages, I should
probably get around to that.
Atila
On Saturday, 14 February 2015 at 17:00:33 UTC, Andrei
Alexandrescu wrote:
There's been recurring discussion about failing constraints not
generating nice error messages.
void fun(T)(T x) if (complicated_condition) { ... }
struct Type(T)(T x) if (complicated_condition) { ... }
If complicated_condition is not met, the symbol simply
disappears and the compiler error message just lists is as a
possible, but not viable, candidate.
I think one simple step toward improving things is pushing the
condition in a static_assert inside type definitions:
void fun(T)(T x) if (complicated_condition) { ... } // no change
struct Type(T)(T x)
{
static assert(complicated_condition, "Informative message.");
...
}
This should improve error messages for types (only). The
rationale is that it's okay for types to refuse compilation
because types, unlike functions, don't overload. The major
reason for template constraints in functions is allowing for
good overloading.
Andrei
