Only letting a string be a certain value: Scriptable Objects

Question

I was working on a scriptable object type for any item in my game and I have a string called s_Type. I only want this string to be a certain value; "food", "story", "collectible", or "nothing". I though about using a class but it would create a loss of mess in my script and I would just prefer using a simple string. How could i return an error if the string's value is not one of the above?

Here is my current script:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PickableItem : ScriptableObject
{
    [Header("Properties")]

    /// <summary>
    ///(string) The name of the item
    /// </summary>
    public string s_ItemName;

    /// <summary>
    /// (string) Description of the item
    /// </summary>
    public string s_Description;

    /// <summary>
    /// (string) types can be as followed: "food", "story", "collectible", "nothing"
    /// </summary>
    public string s_Type;
}

Answer 1

Well, you cannot enforce a rule stating that the string will only be of those words, but if you want, you can use a property, like this:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PickableItem : ScriptableObject
{
    [Header("Properties")]

    /// <summary>
    ///(string) The name of the item
    /// </summary>
    public string s_ItemName;

    /// <summary>
    /// (string) Description of the item
    /// </summary>
    public string s_Description;

    /// <summary>
    /// (string) types can be as followed: "food", "story", "collectible", "nothing"
    /// </summary>
    private string s_Type0;

    public string s_Type
    {
        get
        {
            return s_Type0;
        }

        set
        {
            switch (value)
            {
                case "food":
                case "story":
                case "collectible":
                case "nothing":
                    s_Type0 = value;
                    break;
                default:
                    throw new InvalidArgumentException("Invalid value!");
            }
        }
    }
}

But I would prefer doing it this way:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class PickableItem : ScriptableObject
{
    public enum S_TYPE
    {
        Food,
        Story,
        Collectible,
        Nothing
    }

    [Header("Properties")]
    /// <summary>
    ///(string) The name of the item
    /// </summary>
    public string s_ItemName;

    /// <summary>
    /// (string) Description of the item
    /// </summary>
    public string s_Description;

    /// <summary>
    /// (string) types can be as followed: "food", "story", "collectible", "nothing"
    /// </summary>
    public S_TYPE s_Type;
}

Then you can use s_Type.ToString() to get the string value, and then check accordingly.