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Postings from April 2008
Just surfing, I noticed something about the "D" programming language: " The types of constants need not be specified explicitly as the compiler infers their types <http://en.wikipedia.org/wiki/Type_inference> from the right-hand sides of assignments. const fact_7 = Factorial!(7); " Now in C++, templates can be used to make function return types go along with their argument types, for generic arguments. In Perl 6, I think you would have to arrange to write the return type later rather than sooner to do this: sub foo (::T $a, T $b) is of T and writing it the other way around would violate the one-pass parsing. So, how would you write the constant above in Perl 6, without knowing specifically what foo returned? I'm thinking of a situation where you have foo as a method of a generic class, or otherwise depends on a generic type parameter already. But, it could be an expression not just a function call, and depend on the generic types present in outer scopes in a less-than-simple way. my Type $x = $a ⊗ $b; With C++, I would have to hope that the template writer thought to give the return type of that function a snappy name, rather than just referring to it as an inline conglomeration that involves the generic types. The compiler knows what that type is. How do I refer to it? Can I say, "declare $x to be the type of the right-hand-side", rather than making me name it and checking that I got it right, or leaving it off and not having compile-time checking and optimization for subsequent use of $x ? Here's an idea: a pseudo-type of the form ::?RHSTYPE. I could even capture it for subsequent use, like with generic type parameters: my ::?RHSTYPE ::ProdType $x = $a ⊗ $b; my ProdType $y = $x; --JohnThread Next