The interface type

When you talk to people who have been doing Go for a while, they almost always list the interface as one of their favorite features of the language. The concept of interfaces in Go, similar to other languages, such as Java, is a set of methods that serves as a template to describe behavior. A Go interface, however, is a type specified by the interface{} literal, which is used to list a set of methods that satisfies the interface. The following example shows the shape variable being declared as an interface:

var shape interface { 
    area() float64 
    perim() float64 
} 

In the previous snippet, the shape variable is declared and assigned an unnamed type, interface{area()float64; perim()float64}. Declaring variables with unnamed interface literal types is not really practical. Using idiomatic Go, an interface type is almost always declared as a named type. The previous snippet can be rewritten to use a named interface type, as shown in the following...