Find the type of variable

In this article, you'll learn how to determine the data type of a variable in Go. We cover two primary techniques: using the %T format specifier with fmt.Printf and using the reflect package’s TypeOf function, which can also handle literal values.

Using the %T Format Specifier

The simplest way to discover a variable's data type in Go is by using the %T format specifier with fmt.Printf. In the example below, four variables of different types (integer, string, boolean, and float) are declared. Their values and corresponding data types are then printed.

package main
import "fmt"

func main() {
    var grades int = 42
    var message string = "hello world"
    var isCheck bool = true
    var amount float32 = 5466.54

    fmt.Printf("variable grades = %v is of type %T \n", grades, grades)
    fmt.Printf("variable message = '%v' is of type %T \n", message, message)
    fmt.Printf("variable isCheck = %v is of type %T \n", isCheck, isCheck)
    fmt.Printf("variable amount = %v is of type %T \n", amount, amount)
}

To run the above program, use the following command:

go run main.go

The expected output will be:

variable grades = 42 is of type int
variable message = 'hello world' is of type string
variable isCheck = true is of type bool
variable amount = 5466.54 is of type float32

Using the reflect.TypeOf Function with Literals

The reflect package's TypeOf function is a powerful alternative that works with both variables and literals. In this example, the code shows how to determine the data types of various literals.

package main

import (
    "fmt"
    "reflect"
)

func main() {
    fmt.Printf("Type: %v \n", reflect.TypeOf(1000))
    fmt.Printf("Type: %v \n", reflect.TypeOf("priyanka"))
    fmt.Printf("Type: %v \n", reflect.TypeOf(46.0))
    fmt.Printf("Type: %v \n", reflect.TypeOf(true))
}

Run the program with:

go run main.go

The output is as follows:

Type: int
Type: string
Type: float64
Type: bool

Using the reflect.TypeOf Function with Variables

You can also pass variables into the reflect.TypeOf function to determine their data types. The following example declares two variables and prints both their values and their types.

package main

import (
    "fmt"
    "reflect"
)

func main() {
    var grades int = 42
    var message string = "hello world"

    fmt.Printf("variable grades = %v is of type %v \n", grades, reflect.TypeOf(grades))
    fmt.Printf("variable message = '%v' is of type %v \n", message, reflect.TypeOf(message))
}

Execute the program with:

go run main.go

The expected output is:

variable grades = 42 is of type int
variable message = 'hello world' is of type string

That’s it for this tutorial. In this lesson, you explored two methods to determine the data type of a variable or a literal in Go using both the %T format specifier and the reflect.TypeOf function.

Keep practicing and see you in the next article!