Multiple return values...

[Manu]

On 16 March 2012 04:26, Andrei Alexandrescu
<SeeWebsiteForEmail at erdani.org>wrote:
>
>  A good design should strive to provide general features instead of
>> special cases (E.g. swap is limited to the 2-tuple case). Also, why
>> force an overhead of a function call on such a basic feature as
>> assignment? Is swap usually inlined by the compiler?
>>
>
> Sorry, this is grasping at straws.
>
> 1. swap can be easily generalized to take any number of arguments. I'm
> very happy that's possible, we've expended great efforts on making variadic
> functions as powerful as they are. But nobody asked for swap with many
> arguments until now. Which segues into...
>
> 2. When was the last time you needed to swap arbitrary numbers of
> elements, and so badly and frequently, you needed a new language feature
> for that?
>

This is called a swizzle. And constantly comes up when dealing with
x,y,z,w, or r,g,b,a.
It could just as easily be expressed this way:
  a,b = tuple(b,a); // swap
  r,g,b,a = tuple(a,r,g,b); // swizzle
At which point this multi assignment boils down to the exact same question
of syntax as MRV return assignment. I don't really distinguish this
swap/swizzle from MRV. It all comes back to the return assignment syntax.


> 3. Function overhead is solved by inlining, not by adding new features.
> That improves all functions, not only swap.


Requiring inlining to make it efficient is not enough. The proposed MRV ABI
would solve this not only for inlines, but for all multi-assignment type
constructs, including distant function calls.
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