Go Methods

Internal

• Object-Oriented Programming in Go

Overview

Go allows associating arbitrary behavior with built-in or custom types, which contributes to the object-oriented character of the language. Note that Go is not a fully object-oriented language, it misses type inheritance, for example.

Syntactically, the association of the behavior with the type is done by declaring a function, encapsulating the behavior we want to add to the type, and adding a receiver type to its signature:

func (t ReceiverType) FunctionName(parameters, ...) (return_declaration) {
 ...
}

As result of this association, the function becomes a method of the type.

The declaration is identical to that of a regular function, with the exception of the receiver parameter, which precedes the function name. The receiver parameter gives the method's body access to the instance of the associated type. Aside from its special syntactical position, all other aspects the receiver parameter is identical with the regular parameters of the function.

An aspect that has profound implications on the relationship between the method and the type instance is whether the receiver parameter is a value or a pointer. The deciding factor should be whether the method is intended to change the state of the receiver. Use pointer receivers if you intend to let the method modify the state of the receiver instance. See Deciding between Value or Pointer Receiver.

Receiver

A receiver can be declared to value receiver or a pointer receiver.

Value Receiver

func (t ReceiverType) MethodName(parameters, ...) (return_declaration) {
   ...
}

A value receiver gives access to the copy of the variable the method is invoked on, inside the method. As such, the original variable cannot be modified by the method.

Pointer Receiver

func (t *ReceiverType) MethodName(parameters, ...) (return_declaration) {
   ...
}

A pointer receiver gives access to the variable the method is invoked on, inside the method. As such, the method may modify the state of the original variable.

Deciding between Value or Pointer Receiver

The deciding factor should be whether the method is intended to change the state of the receiver.

Use a pointer receiver if you intend to use the method to modify the state of the receiver instance.

Use a value receiver if the method must not be able to change the state of the receiver instance. Since the receiver argument is passed by value, the original receiver is protected from changes.

Go documentation (Link?) recommends to not mix value and pointer receivers when defining methods for a type.

TODO

Continue and deplete Go_Language_Object_Oriented_Programming#Methods.