Andrei:
>D's constrained templates were introduced on 17 June 2008 and they've been a
>smashing hit. Virtually all of Phobos uses them, and I'm sure a lot of generic
>client code. They take half a minute to explain and solve a difficult problem
>in a very simple manner.<
A template with two constrains makes it less handy to add error messages that
explain why the instantiation has failed:
template Foo(T) if (Pred1!T && Pred2!T) {
...
}
An alternative syntax (same semantics) similar to a (static) precondition
Contract gives more space for error messages:
template Foo(T)
static in {
static assert(Pred1!T, "err msg 1");
static assert(Pred2!T, "err msg 2");
} body {
...
}
Function templates too may have the optional static precondition, before the
optional (run time) precondition.
Bye,
bearophile
