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Question by asdf123 · Aug 17, 2014 at 12:17 AM · listclassintgeneric

Generic List No Sense Problem

Hello, i was making my inventory system for my game and then i had a problem, i created a new script just to make some test i face this no-sense problem:

 using UnityEngine;
     using System.Collections;
     using System.Collections.Generic;
     
     public class Test : MonoBehaviour {
     
         public List<Pig> johnPigList = new List<Pig>();
         public List<Pig> peterPigList = new List<Pig>();
     
         void Start () {
     
             peterPigList = johnPigList;
     
         }
         
         void Update () {
             if (Input.GetKeyDown(KeyCode.G))
                 johnPigList[0].quantity++;
         }
     }
     
     [System.Serializable]
     public class Pig
     {
         public int quantity;
     }

ok, i have two generic lists, johnPigList and then peterPigList, at start peter list is equal to john list, thats ok, but then, when i change the quantity variable, the two list changes too, and this on my mind makes no sense because i defined that these two are equal in the start, so then they are two separed lists.

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Answer by SirCrazyNugget · Aug 17, 2014 at 12:28 AM

on line 12 you're setting the reference of peterPigList to johnPigList, this doesn't clone it just changes the reference (thus losing any reference to the previous peterPigList.

If you want to just clone the list an not change the reference use

 peterPigList = new List<Pig>(johnPigList);
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avatar image Kiwasi · Aug 17, 2014 at 12:31 AM 0
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Spend some time on google understanding the difference between reference types and value types. Will be well worth the effort.

avatar image asdf123 · Aug 17, 2014 at 12:35 AM 0
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sircrazy that doesnt work for me, i have errors.

i tried to put peterPigList = new List(johnPigList);

but is the same thing as peterPigList = johnPigList;

avatar image asdf123 · Aug 17, 2014 at 12:43 AM 0
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i tried to put peterPigList = new List(johnPigList); ***

avatar image Kiwasi · Aug 17, 2014 at 01:02 AM 0
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You probably need the generic type as well.

 peterPigList = new List<Pig>(johnPigList);
avatar image asdf123 · Aug 17, 2014 at 01:08 AM 0
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the console says that the Pig has no constructor

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