lazy variables

[Simen Kjærås]

On Wednesday, 17 October 2018 at 07:32:37 UTC, aliak wrote:
> Hi,
>
> Is there any notion of lazy vars in D (i see that there're 
> parameters)?

What the language doesn't provide, it generally provides the 
tools to make:

struct Lazy(T) {
     T delegate() _payload;
     this(lazy T t) {
         _payload = () => t;
     }
     T get() {
         return _payload();
     }
     alias get this;
}

int fun() {
     n++;
     return 2;
}

int n;

unittest {
     Lazy!int a = 1 + fun();
     assert(n == 0); // Ensure fun hasn't been called.
     auto b = a + 2;
     assert(b == 5); // Ensure calculation is correct.
     assert(n == 1); // Ensure fun has been called.
}

--
   Simen