go iterate and mutate precautions / published by https://github.com/dacr/code-examples-manager #5d53f10b-6fd6-4ebe-ad5d-b768adf3d8c3/b0e2eaaf1224d20a56263cc4d55b1be3b59443d3

iterate-and-mutate.go

/*?sr/bin/true; exec /usr/bin/env nix-shell -p go --run "go run $0" #*/
// summary : go iterate and mutate precautions
// keywords : go, iterate, mutate, structure, @testable
// publish : gist
// authors : David Crosson
// license : Apache NON-AI License Version 2.0 (https://raw.githubusercontent.com/non-ai-licenses/non-ai-licenses/main/NON-AI-APACHE2)
// id : 5d53f10b-6fd6-4ebe-ad5d-b768adf3d8c3
// created-on : 2025-03-28T08:47:47+01:00
// managed-by : https://github.com/dacr/code-examples-manager
// run-with : nix-shell -p go --run "go run $file"
package main

import "fmt"

// ======================================================================================================

type Someone struct {
	FirstName string
	LastName  string
	Alias     string
	Age       int
}

var people = []Someone{
	{FirstName: "John", LastName: "Doe", Alias: "-", Age: 30},
	{FirstName: "Barbara", LastName: "Doe", Alias: "-", Age: 25},
	{FirstName: "Gill", LastName: "Doe", Alias: "-", Age: 20},
}

func main() {
	// -------------------------------------------------
	for _, someone := range people {
		// someone has been copied !!!
		someone.Alias = someone.FirstName[0:1] + someone.LastName[0:1]
		// SO only the copy has been modified ! not the original one
	}
	for index, someone := range people {
		fmt.Println(index, someone)
	}
	// -------------------------------------------------
	for index, someone := range people {
		people[index].Alias = someone.FirstName[0:1] + someone.LastName[0:1] // !!!!
	}
	for index, someone := range people {
		fmt.Println(index, someone)
	}
}