Blog / Go Language Spec

Predeclared types

February 16, 2023

Types

The language predeclares certain type names. Others are introduced with type declarations or type parameter lists. Composite types—array, struct, pointer, function, interface, slice, map, and channel types—may be constructed using type literals.

Type declarations, type parameter lists, and type aliases are coming up later, so today we’re focused on the predeclared types.

The list of predclared types would appear near the beginning of most intro to Go books (I would know, I just read and reviewed 11 of them!). In the Go spec, they appear about a third of the way through. So we’re jumping ahead to enumerate them. These are all of the predeclared, or “basic” types in Go.

Type Name Description
any Alias for interface{}, the empty interface
bool Boolean, possible values are true and false
byte Alias for uint8
comparable Denotes all non-interface types that are strictly comparable
complex64 A 64-bit complex number
complex128 A 128-bit complex number
error Interface type used to report errors
float32 32-bit floating point number
float64 64-bit floating point number
int A 32- or 64-bit signed integer*
int8 An 8-bit signed integer
int16 A 16-bit signed integer
int32 A 32-bit signed integer
int64 A 64-bit signed integer
rune Alias for int32, A Unicode codepoint
string A string of Unicode characters
uint A 32- or 64-bit unsigned integer*
uint8 An 8-bit unsigned integer
uint16 A 16-bit unsigned integer
uint32 A 32-bit unsigned integer
uint64 A 64-bit unsigned integer
uintptr An unsigned integer large enough for a pointer value*

* The size of these types is architecture-dependent.

Quotes from The Go Programming Language Specification, Version of January 19, 2023

Share this

Related Content

Declaring variable types

Today I’ll be love coding again. I hope you can join me! I’ll be working on the backlog for my open-source CouchDB SDK, https://kivik.io/. First some light refactoring, then adding a long-missing feature. Join me to see how many mistakes a senior Go dev makes while coding. We ended last week with a look at variable declarations. Today we continue that, with a look at how a variable’s type is determined.

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.

Type definitions

Some of the minutiae we’ve gone over about underlying types, and type identity are finally starting to come together… Type definitions A type definition creates a new, distinct type with the same underlying type and operations as the given type and binds an identifier, the type name, to it. TypeDef = identifier [ TypeParameters ] Type . The new type is called a defined type. It is different from any other type, including the type it is created from.