How are Interfaces Represented in Go: (Value, Type) Pair or Method Table?

Understanding Interface Representation in Go

When working with interfaces in Go, it's important to grasp their underlying representation. Two key resources shed light on this topic, but their perspectives differ.

The "Laws of Reflection" article (http://blog.golang.org/laws-of-reflection) introduces the concept of an interface containing a (value, type) pair, as seen in the example of r io.Reader. This pair includes the value tty and its type *os.File.

Alternatively, the other article emphasizes that interfaces contain only methods for satisfying the interface's specification. In the example of Stringer holding type Binary, the itable (interface method table) lists only the methods necessary for the String implementation, excluding other methods defined on the Binary type.

To reconcile these perspectives, consider interfaces in Go as "wrapper objects" at runtime. They provide information about another object, the itable, which guides the runtime in executing methods on the wrapped object. For instance, when calling Read on r, the runtime uses the itable to jump to the corresponding function within the os.File type layout.

Reflection, as described in the "Laws of Reflection" article, provides a convenient way to explore this representation by exposing the (value, type) pair through the reflect.ValueOf and reflect.TypeOf methods.

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