__has_side_effects

[Andrei Alexandrescu]

On 4/1/18 2:22 AM, Uknown wrote:
> On Sunday, 1 April 2018 at 05:27:38 UTC, Uknown wrote:
>> [...]
>>
>> I knew I was missing something. Fixed it, thanks
>>
>> https://run.dlang.io/is/tZeZrP
> 
> Sorry for the spam, but I also managed to miss `immutable`, `const` and 
> when T has mutable indirections
> 
> Final version that I'm sure covers all the cases:
> 
> https://run.dlang.io/is/kGoU4X

That's a great initiative, and a worthy trait for the stdlib. I think 
you'd have an easier time if you reasoned from the other end. A function 
is strongly pure if all of the following are true:

* Each parameter:
   - is immutable, OR
   - can be converted automatically to immutable (i.e. has no mutable 
indirections) AND is passed by value
* The return type:
   - is immutable, OR
   - can be converted automatically to immutable

(We don't want to give const this much power yet for other reasons.)

The template should support taking the function name as a string, too, 
and the parameter types so as to easily distinguish across overloads.

This would be a great addition to std.traits. Once we have it, we'll 
have a precise unified definition of strongly pure across the language 
spec and the stdlib definition. Please follow up, thanks!


Andrei