<PackageReference Include="NETStandard.Library" Version="2.0.0" />

System.Lazy<T>

public class Lazy<T>
namespace System { public class Lazy<T> { public bool IsValueCreated { get; } public T Value { get; } public Lazy(); public Lazy(bool isThreadSafe); public Lazy(Func<T> valueFactory); public Lazy(Func<T> valueFactory, bool isThreadSafe); public Lazy(Func<T> valueFactory, LazyThreadSafetyMode mode); public Lazy(LazyThreadSafetyMode mode); } }