Implementation of Interfaces

Testing if a value implements an interface

This is a special case of the type assertion: suppose v is a value, and we want to test whether it implements the Stringer interface. This can be done as follows:

type Stringer interface { String() string }
if sv, ok := v.(Stringer); ok {
  fmt.Printf("v implements String(): %s\n", sv.String()); // note: sv, not v
}

An interface is a kind of contract, which the implementing type(s) must fulfill. Interfaces describe the behavior of types, specifying what types can do. They completely separate the definition of what an object can do from how it does it, allowing distinct implementations to be represented at different times by the same interface variable, which is what polymorphism essentially is. Writing functions so that they accept an ...