Light, allocation-free (but not thread-safe) Lazy implementation.

LightLazy.cs

public static class LightLazy
{
    public static LightLazy<TItem> Create<TItem>(Func<TItem> itemConstructor)
        where TItem : class
        => new LightLazy<TItem>(itemConstructor);
}

public struct LightLazy<TItem>
    where TItem : class
{
    private readonly Func<TItem> _itemConstructor;

    public LightLazy(Func<TItem> itemConstructor)
    {
        _itemConstructor = itemConstructor;
        ItemOrNull = null;
    }

    /// <summary>Does not construct the item.</summary>
    public TItem ItemOrNull { get; private set; }

    /// <summary>Constructs the item if not yet constructed.</summary>
    public TItem Item => ItemOrNull ?? (ItemOrNull = _itemConstructor());

    public bool ItemConstructed => ItemOrNull != null;
}