Receiver uniqueness

September 4, 2023

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Method declarations

A non-blank receiver identifier must be unique in the method signature. If the receiver’s value is not referenced inside the body of the method, its identifier may be omitted in the declaration. The same applies in general to parameters of functions and methods.

No surprises here. We already know that function parameters and named return values must be unique within the function signature. The same is true for the receiver.

func (f Foo) Frobnicate(f filename) error { // Invalid, `f` is not unique
	/* ... */

Further, the receiver name can be either blank, or omitted (preferred), if it’s not referenced within the body of the method. This same rule applies to function parameters that are not referenced.

func (_ Dog) Speak() string { // Blank receiver, since it's not used
	return "woof"

func (Cat) Speak() string { // Receiver name omitted entirely, since it's not used
	return "meow"

Quotes from The Go Programming Language Specification Version of August 2, 2023

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Type parameters in method definitions

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Method declarations

Now that we’ve covered function declarations, let’s discuss the more nuanced topic of method declarations, which can be thought of as special case of of function declarations. Method declarations A method is a function with a receiver. A method declaration binds an identifier, the method name, to a method, and associates the method with the receiver’s base type. MethodDecl = "func" Receiver MethodName Signature [ FunctionBody ] . Receiver = Parameters .