Go for Developers: Defined Types, Pointers and Functions

Introduction

In the previous part we covered the most common data structures in Go: arrays, slices, maps, and structs. We declared them using Type Literals, which are used to create Unnamed Types. Type Literals have their trade-offs, which will be discussed later in this article. This article will cover Defined Types, Pointers, and Functions.

Defined Types, are part of Named Types. You can look at the top-level split in the Basic Types section in the article.

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Defined Types

In Go, defined types are the types you create yourself using the type keyword. Defined types prevent accidental misuse of semantically different values. A type definition creates a new, distinct type that is different from any other type, even if they share the same underlying structure:

type UserID int32
type ProductID int32

var u UserID = 1
var p ProductID = 1

// compile error: mismatched types
fmt.Println(u == p)

By treating UserID and ProductID as different types, Go prevents you from accidentally passing a product's ID into a function that expects a user's ID.