Type inference

Learn how Go infers the type from the right side.

Type inference

Go can infer the type of the left side from the right side. Writing x := 5, Go understands x is an int. Writing y := 3.14, it infers y as float64.

Type inference keeps code concise and readable. But sometimes the type is written explicitly; especially when a specific integer type (e.g. int32) is needed.

For strings, s := "hello" is enough; no need for var s string. Inference happens at compile time; it has no runtime cost.

Inference principles

Type inference follows clear rules: integers become int, decimals float64, characters rune, strings string.

With multiple returns, each value's type is inferred separately. For example a, b := 1, "x" gives a int, b string.

Inference works only at compile time; the type does not change at runtime. Go is statically typed; once set, the type stays.

Exercise Inferred types

Declare a := 5, b := 2.5, c := 'x', d := "go" and print the types Go inferred with fmt.Printf("%T %T %T %T\n", a, b, c, d).

Show example solution

package main

import "fmt"

func main() {
    a := 5
    b := 2.5
    c := 'x'
    d := "go"
    fmt.Printf("%T %T %T %T\n", a, b, c, d)
}

Test yourself

What is the type of x in x := 3.14?
- float64
- int
- float32
- decimal
Show answer

float64 — 3.14 is inferred as float64.

Inference example

If x := 5 then x's type is ____.

Show answer

If x := 5 then x's type is int.

Match the inferred types

5

int
3.14

float64
'a'

rune
"x"

string

Next lesson: Summary - Variables

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