WaitForSeconds manager that reuses instances to avoid GC in Unity

BetterWaitForSeconds.cs

using System.Collections.Generic;
using UnityEngine;

public static class BetterWaitForSeconds
{
	private class WaitForSeconds : CustomYieldInstruction
	{
		private float waitUntil;
		public override bool keepWaiting
		{
			get
			{
				if( Time.time < waitUntil )
					return true;

				Pool( this );
				return false;
			}
		}

		public void Initialize( float seconds )
		{
			waitUntil = Time.time + seconds;
		}
	}

	private class WaitForSecondsRealtime : CustomYieldInstruction
	{
		private float waitUntil;
		public override bool keepWaiting
		{
			get
			{
				if( Time.realtimeSinceStartup < waitUntil )
					return true;

				Pool( this );
				return false;
			}
		}

		public void Initialize( float seconds )
		{
			waitUntil = Time.realtimeSinceStartup + seconds;
		}
	}

	private const int POOL_INITIAL_SIZE = 4;

	private static readonly Stack<WaitForSeconds> waitForSecondsPool;
	private static readonly Stack<WaitForSecondsRealtime> waitForSecondsRealtimePool;

	static BetterWaitForSeconds()
	{
		waitForSecondsPool = new Stack<WaitForSeconds>( POOL_INITIAL_SIZE );
		waitForSecondsRealtimePool = new Stack<WaitForSecondsRealtime>( POOL_INITIAL_SIZE );

		for( int i = 0; i < POOL_INITIAL_SIZE; i++ )
		{
			waitForSecondsPool.Push( new WaitForSeconds() );
			waitForSecondsRealtimePool.Push( new WaitForSecondsRealtime() );
		}
	}

	public static CustomYieldInstruction Wait( float seconds )
	{
		WaitForSeconds instance;
		if( waitForSecondsPool.Count > 0 )
			instance = waitForSecondsPool.Pop();
		else
			instance = new WaitForSeconds();

		instance.Initialize( seconds );
		return instance;
	}

	public static CustomYieldInstruction WaitRealtime( float seconds )
	{
		WaitForSecondsRealtime instance;
		if( waitForSecondsRealtimePool.Count > 0 )
			instance = waitForSecondsRealtimePool.Pop();
		else
			instance = new WaitForSecondsRealtime();

		instance.Initialize( seconds );
		return instance;
	}

	private static void Pool( WaitForSeconds instance )
	{
		waitForSecondsPool.Push( instance );
	}

	private static void Pool( WaitForSecondsRealtime instance )
	{
		waitForSecondsRealtimePool.Push( instance );
	}
}