Difference between new and make in Golang #

In Go, make and new are built-in functions used for memory allocation.

• make not only allocates memory but also initializes the data, which is necessary because the data types supported by make (like slices, maps, and channels) require initialization before use.
• On the other hand, new allocates memory space that is filled with zero values.
• new allocates a single block of memory, while make may allocate multiple blocks of memory.

new #

• Usage: For basic types like integers, structs, and arrays.
• Returns: A pointer to the allocated type.

Example:

package main

import "fmt"

func main() {
    p := new(int)
    fmt.Println(*p) // 0
    *p = 42
    fmt.Println(*p) // 42

    type Person struct {
        Name string
        Age  int
    }

    person := new(Person)
    fmt.Println(*person) // { 0}
    person.Name = "John"
    person.Age = 30
    fmt.Println(*person) // {John 30}
}

make #

• Usage: For slices, maps, and channels.
• Returns: The initialized type itself.

Example:

package main

import "fmt"

func main() {
    slice := make([]int, 5)
    fmt.Println(slice) // [0 0 0 0 0]
    for i := range slice {
        slice[i] = i + 1
    }
    fmt.Println(slice) // [1 2 3 4 5]

    m := make(map[string]int)
    fmt.Println(m) // map[]
    m["one"] = 1
    m["two"] = 2
    fmt.Println(m) // map[one:1 two:2]

    ch := make(chan int, 2)
    fmt.Println(len(ch)) // 0
    ch <- 1
    ch <- 2
    fmt.Println(len(ch)) // 2
}

Key Differences #

1. Types: new for any type, make for slices, maps, and channels.
2. Return Value: new returns a pointer, make returns an initialized value.
3. Initialization: new allocates zeroed storage, make allocates and initializes.