gistfile1.cs

public class CachedValue<T>
{
    private bool _hasValue;
    private T _value;

    private Func<T> _getter;

    public T Value => _hasValue ? _value : (_value = _getter());

    public CachedValue(Func<T> getter)
    {
        _getter = getter;
    }

    public static implicit operator CachedValue<T>(Func<T> getter)
    {
        return new CachedValue<T>(getter);
    }
}

public class Hoge
{
    private CachedValue<bool> Is64Bit =>
        new Func<bool>(() => Marshal.SizeOf<IntPtr>() == 8);

    // こう書きたい人生だった
    //private CachedValue<bool> Is64Bit =>
    //    () => Marshal.SizeOf<IntPtr>() == 8;
}