Go Concepts - The Type System

Internal

• Concepts

Overview

Go is statically typed. Go designers tried to alleviate some of the "heaviness" associated with statically typed languages and made it "feel" like a dynamic language. For example Go uses local type inference, which eliminates the need to specify the type unnecessarily in program, the compiler figures it out.

Go is strongly typed meaning that yes cannot be unsafely coerced into other types they're not, or at least without programmer giving explicit permission. In JavaScript, for example, implicit conversion is done based on complicated rules that are not always easy to remember.

For more details on typing, see static typing vs. dynamic typing and strong typing vs. loose typing.

Type Definition

Type Definition

Zero Value

Zero value for a specific type: 0 for ints, 0.0 for floats, "" for strings, false for Booleans and nil for pointers. For reference types, their underlying data structures are initialized to their zero values.

Function Types

A function is member of a function type. The function type is defined by its signature.

Example: func(int) int.

// a variable of type func(int) int is declared
var f func(int) int;

// the variable is initialized with an actual function
f = func(i int) int {
    return i + 1
}

Pointer Types

A pointer type is declared using the dereference operator * placed in front of the target type - the type of the stored value:

*int

We cannot do pointer arithmetic. Assuming ptr is a *int, we cannot do ptr + 1 (compilation error message: invalid operation: ptr + 1 (mismatched types *int and int)) and we can't do ptr + ptr2 (compilation error message: invalid operation: ptr + ptr2 (operator + not defined on pointer)).

For more details, see pointers.

User-Defined Types

The user-defined types are introduced by the type keyword. There are two kinds of user-defined types: structs and interfaces.

Structs

Structs

Interfaces

Interfaces

Conversion Between Types

In order to convert between types, the type name is used like a function:

var f float64 = 5.0
var i int = 5
...
result = f / float64(i)

This is equivalent with Java cast.

Also see:

Conversion between bytes and strings

Duck Typing

For more details on duck typing go here.