namespace System;
/// A value set once, by whoever comes first (Rust's `OnceCell`/`OnceLock`,
/// .NET's `LazyInitializer`); thread-safe.
[Intrinsic]
public readonly sealed class Once<T> {
public Once() {}
/// Sets it unless it's set: whether this did.
public readonly bool TrySet(T value);
/// Its value, made by `make` if it's not set yet (once, whoever asks).
public readonly T GetOrInit(Func<T> make);
/// Its value, `null` until it's set.
public readonly T? Get();
public bool IsSet { get; }
}