minimal evaluation

[Daniel Keep]

Qian Xu wrote:
> Hi All,
> 
> Is minimal evaluation always enabled in D?
> 
> I want to write a function IsNull(), so that I can check the precondition as
> follows:
> 
>   if (isNull(foo) ||
>       isNull(foo.getBar) ||
>       isNull(foo.getBar.getBar2)
>   {
>     return false;
>   }
>   // normal code goes here
> 
> If an argument is null, the IsNull() will return false. Internally it will
> be logged to console as well.
> 
> But I am not sure, if dmd-compiler generates code without minimal evaluation
> in some cases. If minimal evaluation is not always enabled. I cannot do
> precodition check in my way. 
> 
> --Qian

I can't find anything in the language spec that mandates it, but I do
believe the compiler supports boolean short-circuiting (that's what I've
always seen it called.)  There was a bug report a long time ago that
this didn't happen for CTFE, and it was fixed as a bug, so I assume
short-circuiting is the intended behaviour.

Perhaps this should go in the spec; it's certainly something I expect
from any half-sane language.

  -- Daniel