A fast, atomic lazy that only allows a single publish operation to happen, but allows executions to occur concurrently. Does not cache exceptions. Designed for use with T types that are IDisposable or are otherwise considered to be expensive to allocate. Read the full explanation here: https://github.com/Aaronontheweb/FastAtomicLazy#rationale

public sealed class FastLazy<S, T>

[<SealedAttribute>]
type FastLazy<'S, 'T> =  class end