Boldly Go

2 min read

Interface examples with type elements

Let’s look at some interface examples from the spec: General interfaces … // An interface representing only the type int. interface { int } // An interface representing all types with underlying type int. interface { ~int } // An interface representing all types with underlying type int that implement the String method. interface { ~int String() string } // An interface representing an empty type set: there is no type that is both an int and a string.

Go Language Spec

1 min read

Interfaces don't contain interfaces

As we learned recently, Go interface elements may contain a type term of a non-interface type. It’s worth re-iterating that these are non-interface types. In particular, as the spec states: General interfaces … By construction, an interface’s type set never contains an interface type. That is to say, that the following is invalid: type interface foo { /* some interface elements */ } type interface bar { foo } Actually, I lied.

Go Language Spec

1 min read

"Duck Typing" defined

I’ve already introduced the concept of duck typing, but now we have more or less a formal definition: General interfaces … The quantification “the set of all non-interface types” refers not just to all (non-interface) types declared in the program at hand, but all possible types in all possible programs, and hence is infinite. Similarly, given the set of all non-interface types that implement a particular method, the intersection of the method sets of those types will contain exactly that method, even if all types in the program at hand always pair that method with another method.