How does Golang function return value manage memory?

Memory management of function return values ​​follows value semantics. Functions pass parameters and return values ​​by value. Changes to the copy do not affect the original variable. Pointer passing allows functions to directly modify the original variable. By applying these concepts, slice copying can be implemented efficiently, directly modifying elements in the target slice and avoiding the creation of new copies.

Memory management of function return values ​​in Go

In Go, the memory management of function return values ​​is affected by value semantics, which is an important A language feature that states that a variable always contains a copy of its value.

Value passing

Go functions pass parameters and return values ​​through value passing. This means that a copy is created and passed, not a reference to the original value.

For example, the following code defines an Add function that accepts two value type parameters and returns a value type result:

package main

func Add(a, b int) int {
    return a + b
}

func main() {
    x := 1
    y := 2
    sum := Add(x, y)
    fmt.Println(sum) // 输出：3
}

In Add Inside the function, copies of x and y are passed. Any changes made to these copies will not affect the value of the original variable. So when Add returns, it returns a copy of the sum of x and y.

Pointer passing

You can avoid creating a copy during value passing by passing a value of pointer type. This allows the function to directly modify the value of the original variable.

For example, the following code defines an Inc function that accepts a parameter of pointer type and increments it:

package main

import "fmt"

func Inc(ptr *int) {
    *ptr++
}

func main() {
    x := 1
    Inc(&x)
    fmt.Println(x) // 输出：2
}

In the Inc function , the value of pointer ptr is the address of original variable x. Changes to *ptr are applied directly to the original variable. Therefore, when Inc returns, the value of x has been incremented.

Practical Case: Implementing Slice Copy

We can apply these concepts to actual combat, such as implementing a function that copies a slice without creating a newly allocated copy:

package main

func CopySlice(dst, src []int) {
    for i := range src {
        dst[i] = src[i]
    }
}

func main() {
    src := []int{1, 2, 3}
    dst := make([]int, len(src))
    CopySlice(dst, src)
    fmt.Println(dst) // 输出：[]int{1, 2, 3}
}

In the CopySlice function, we use pointer arithmetic to directly modify the elements in the dst slice, thereby avoiding creating a copy of the src slice.

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