Blog / Go Language Spec

Every type has a method set

June 8, 2023

Method sets

The method set of a type determines the methods that can be called on an operand of that type. Every type has a (possibly empty) method set associated with it.

Wait right there.

That bears repeating

Every type has a (possibly empty) method set

Let that sink in.

Every type has a method set.

This surprises many newcomers, as in many langauges, we’re accustomed to thinking of only “objects” having methods. And many (somewhat erroneously) translate this to the idea that “in Go, we use structs as objects, so only structs can have methods.”

But in Go, we can define methods on any type, not just structs.

Quotes from The Go Programming Language Specification Version of December 15, 2022

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Related Content

Defining method sets

Recall that every type in Go has a method set. Let’s examine how that’s defined: Method sets … Every type has a (possibly empty) method set associated with it: The method set of a defined type T consists of all methods declared with receiver type T. type S struct { /* Possibly some fields */ } // Foo() is a member of the method set of `S`, because it has a receiver type `S`.

Types with methods

Type definitions … A defined type may have methods associated with it. It does not inherit any methods bound to the given type, but the method set of an interface type or of elements of a composite type remains unchanged: // A Mutex is a data type with two methods, Lock and Unlock. type Mutex struct { /* Mutex fields */ } func (m *Mutex) Lock() { /* Lock implementation */ } func (m *Mutex) Unlock() { /* Unlock implementation */ } // NewMutex has the same composition as Mutex but its method set is empty.

Where declarations are allowed

First, a big thanks to everyone who showed up for yesterday’s first Boldly Go Live stream. We had some audio problems, which I promise to fix before the next one. But otherwise it was a success, with some great discussion. You can catch the replay if you missed it. Here we are at the formal description of declaration syntax. Declarations and scope … Declaration = ConstDecl | TypeDecl | VarDecl .