Lazy struct

Code:

    struct Lazy<T>
    {
        T value;
        bool init;
        Func<T> factory;

        public Lazy(Func<T> f)
        {
            factory = f;
            init = false;
            value = default(T);
        }

        public T Value
        {
            get
            {
                if (init) return value;
                else
                {
                    init = true;
                    return value = factory();
                }
            }
        }
    }

Variant with a single argument
is useful when we want to use a non-local function and don't want to use closure (for better performance)

Code:

    struct Lazy<TVal, TArg>
    {
        TVal value;
        TArg arg;
        bool init;
        Func<TArg, TVal> factory;

        public Lazy(Func<TArg, TVal> f, TArg arg)
        {
            factory = f;
            init = false;
            value = default(TVal);
            this.arg = arg;
        }

        public TVal Value
        {
            get
            {
                if (init) return value;
                else
                {
                    init = true;
                    return value = factory(arg);
                }
            }
        }
    }