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Re:Merging In The GNU D Language Compiler To GCC by sambeau on Monday October 10, 2011 @07:07AM (#3093226)
It is more subtle and powerful than that.

By placing the contract at the use of a type with an interface rather than at the declaration of a type you effectively introduce a form of duck typing to a static language.

You can write an interface for a type long after the type has been declared (or been declared by someone else). Interfaces can be defined and used without having to go back and change existing code. This is very lightweight.

Re:Merging In The GNU D Language Compiler To GCC by pjmlp on Tuesday October 11, 2011 @01:49AM (#3097315)
Still, there are a few functional programming languages that offer similar concepts. Scala is one of them, as a few in the ML family.