Simple wrapper classes for handling layer related operations in Unity.

LayerIDs.cs

using UnityEngine;

/// <summary>
/// Convenience class for handling layer related operations and lookups in Unity.
/// </summary>
public readonly struct UnityLayer
{
    /// <summary>
    /// Name of the layer as defined in the Tags and Layers window in Unity.
    /// </summary>
    public readonly string Name;

    /// <summary>
    /// Bitmask value to be used when constructing a <see cref="LayerMask"/> for
    /// operations such as raycasts.
    /// </summary>
    public readonly int Mask;

    /// <summary>
    /// ID for doing lookups and comparisons such as with <see cref="GameObject.layer"/>.
    /// </summary>
    public readonly int ID;

    /// <param name="name">Name of the layer as it appears in the "Tags and Layers" window.</param>
    public UnityLayer(string name)
    {
        Name = name;
        Mask = LayerMask.GetMask(name);
        ID = LayerMask.NameToLayer(name);
    }
}

/// <summary>
/// Wrapper class for all the layers that the game uses. Can be accessed from anywhere.
/// </summary>
public static class LayerIDs
{   
    // These are some of the layers I use. Add/remove layers as needed for your game.
    public static readonly UnityLayer Default = new UnityLayer("Default");
    public static readonly UnityLayer Terrain = new UnityLayer("Terrain");
    public static readonly UnityLayer Building = new UnityLayer("Building");
}

/* ==================================================
// Simple examples for using the LayerID class:

// Assign a layer to an object.
coolObject.layer = LayerIDs.Building.ID;

// Check if something is on a given layer.
var isHitbox = coolObject.layer == LayerIDs.Hitbox.ID;

// Construct a LayerMask for use in things like Raycasts.
var hitMask = LayerIDs.Terrain.Mask | LayerIDs.Hitbox.Mask;
// ================================================*/

Suggestions:

• public struct UnityLayer // no allocation
• public readonly string Name; // constant
• public static readonly UnityLayer Default = ...

There's no reason these need to be mutable. Good catch.