Pure tail call optimization
deadalnix
deadalnix at gmail.com
Sat Nov 2 19:11:18 PDT 2013
On Friday, 1 November 2013 at 18:12:28 UTC, Simen Kjaeraas wrote:
> Today, while playingly adding const annotations to std.bigint,
> I noticed that I ended up with a few casts - or more
> specifically, assumeUniques.
>
> Now, the interesting thing was the pattern they formed. Almost
> invariably, it's like this:
> BigUint foo() pure {
> uint[] result;
> //...
> return BigUint(assumeUnique(result));
> }
>
> Now, had I instead returned uint[] directly, an external
> function could take advantage of the fact that the function was
> pure:
>
> uint[] fooImpl() pure {
> uint[] result;
> //...
> return result;
> }
>
> BigUint foo() pure {
> return BigUint(fooImpl());
> }
>
> As one can clearly see, this removes the need for assumeUnique.
> However, it also complicates the design. Lastly, given that the
> compiler already knows the return value of a pure function is
> magical, it seems it should be possible to exploit that also
> here.
>
> I will therefore suggest that when the return statement of a
> pure function consists of a single call to another pure
> function, and there is no possibility of aliasing of arguments,
> the arguments to that call may be treated as immutable.
>
> Destroy.
>
> --
> Simen
isolated. I think that will become my answer to most problem as
of now :D
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