Golang clear function

last modified May 8, 2025

This tutorial explains how to use the clear built-in function in Go. We'll cover its usage with slices and maps through practical examples.

The clear function was introduced in Go 1.21 to zero out elements in slices and delete all entries from maps. It provides a clean way to reset collections to their zero state.

In Go, clear operates differently based on the type it's applied to. For slices, it sets elements to their zero value. For maps, it removes all keys.

Clearing a slice

The simplest use of clear resets all elements in a slice to their zero values. This example demonstrates basic slice clearing.
Note: The slice length remains unchanged; only elements are zeroed.

basic_clear_slice.go

package main

import "fmt"

func main() {
    numbers := []int{1, 2, 3, 4, 5}
    fmt.Println("Before clear:", numbers)
    
    clear(numbers) // Zero out all elements
    
    fmt.Println("After clear:", numbers)
    fmt.Println("Slice length:", len(numbers))
}

The clear function sets all integer elements to 0. The slice's length and capacity remain unchanged after the operation.

Clearing a map

When applied to maps, clear removes all key-value pairs. This example shows map clearing in action.

clear_map.go

package main

import "fmt"

func main() {
    userRoles := map[string]string{
        "alice": "admin",
        "bob":   "editor",
        "eve":   "viewer",
    }
    
    fmt.Println("Before clear:", userRoles)
    fmt.Println("Map length:", len(userRoles))
    
    clear(userRoles) // Remove all entries
    
    fmt.Println("After clear:", userRoles)
    fmt.Println("Map length:", len(userRoles))
}

The map becomes empty after clearing. Unlike slice clearing, this actually removes all entries rather than zeroing values.

Clearing a slice of structs

clear works with complex types by setting all fields to their zero values. This example demonstrates clearing a slice of structs.

clear_struct_slice.go

package main

import "fmt"

type Point struct {
    X, Y int
    Name string
}

func main() {
    points := []Point{
        {1, 2, "A"},
        {3, 4, "B"},
        {5, 6, "C"},
    }
    
    fmt.Println("Before clear:", points)
    clear(points)
    fmt.Println("After clear:", points)
}

All fields of each struct in the slice are set to their zero values. Numeric fields become 0, and string fields become empty strings.

Clearing a map with interface values

clear handles maps with interface values by completely removing all entries. This example shows clearing a map with mixed value types.

clear_interface_map.go

package main

import "fmt"

func main() {
    data := map[string]interface{}{
        "name":    "Alice",
        "age":     30,
        "active":  true,
        "scores":  []int{90, 85, 95},
    }
    
    fmt.Println("Before clear:", data)
    fmt.Println("Map length:", len(data))
    
    clear(data)
    
    fmt.Println("After clear:", data)
    fmt.Println("Map length:", len(data))
}

The map is completely emptied regardless of the value types it contained. This is different from slice behavior where elements are zeroed.

Clearing a portion of a slice

We can clear specific portions of a slice using slicing. This example shows how to clear a range of elements.

clear_slice_portion.go

package main

import "fmt"

func main() {
    data := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
    fmt.Println("Original:", data)
    
    // Clear elements 3 through 7 (inclusive)
    clear(data[3:8])
    
    fmt.Println("After clearing portion:", data)
}

Only the specified slice portion is cleared. The rest of the slice remains unchanged. This technique is useful for partial resets.

Source

Go language specification

This tutorial covered the clear function in Go with practical examples of clearing slices and maps in various scenarios.

Author

My name is Jan Bodnar, and I am a passionate programmer with extensive programming experience. I have been writing programming articles since 2007. To date, I have authored over 1,400 articles and 8 e-books. I possess more than ten years of experience in teaching programming.

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