Finding the type of a variable in Go

The Problem

I don’t know how to identify the type of a variable in Go.

The Solution

You can use either the %T verb from the fmt package or the Go type switches to determine variable types in Go.

For the purposes of print debugging, you can get the string representation of a variable using the fmt package with the %T verb:

package main

import "fmt"

func main() {
	example := "some string"
	fmt.Printf("variable's type is: %T", example)
}

This prints:

variable's type is: string

However, if you need to identify the type of a variable for a specific purpose, it is best to use a type switch. Type switches are similar to normal switch statements, only they switch types rather than values:

package main

import "fmt"

func main() {
	printType("example") // Prints "received a string".
	printType(42)        // Prints "received an int".
	printType(4.2)       // Prints "received an unknown type".
}

func printType(value any) {
	switch value.(type) {
	case int:
		fmt.Println("received an int")
	case string:
		fmt.Println("received a string")
	default:
		fmt.Println("received an unknown type")
	}
}

The reflect package can also be used to inspect the type information of a variable more deeply:

package main

import (
	"fmt"
	"reflect"
)

func main() {
	example := 42

	reflectType := reflect.TypeOf(example)

	fmt.Printf("example type bits: %d, size (in bytes): %d, string representation: %s", reflectType.Bits(), reflectType.Size(), reflectType.String())
}

This prints:

example type bits: 64, size (in bytes): 8, string representation: int

While the reflect package is interesting and contains detailed information about the types in your program, it is not performant and you should avoid using it in production environments when possible.

Further reading

• The Go reflect package
• The Laws of Reflection blog post