lazy variables

[aliak]

On Thursday, 18 October 2018 at 14:16:56 UTC, Simen Kjærås wrote:
> 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

yes! perfect! Thank you