Why don't changes made to a struct via a method persist?

Question

I\'m trying to understand why the following test code is not working as expected:

package main

import (
    \"fmt\"
    \"strings\"
)

type Test struct {
           


        

Answer 1

The AddString method is using a value (copy) receiver. The modification is made to the copy, not the original. A pointer receiver must be used to mutate the original entity:

package main

import (
        "fmt"
)

type Test struct {
        someStrings []string
}

func (t *Test) AddString(s string) {
        t.someStrings = append(t.someStrings, s)
        t.Count() // will print "1"
}

func (t Test) Count() {
        fmt.Println(len(t.someStrings))
}

func main() {
        var test Test
        test.AddString("testing")
        test.Count() // will print "0"
}

Playground

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Output

1
1