Should reduce take range as first argument?

[Andrei Alexandrescu]

On 5/14/12 4:10 PM, Justin Whear wrote:
> In its current form, std.algorithm.reduce takes optional seed value(s)
> for the accumulator(s) as its first argument(s). This breaks the nice
> chaining effect made possible by UFCS:
>
> Works:
> -----------------------------------------
> auto foo = reduce!((string s, string x) =>  s ~= x)("BLAH", args.map!(x =>
> x[1..$-1]));
> -----------------------------------------
>
> Doesn't work, but looks much nicer:
> -----------------------------------------
> auto foo = args.map!(x =>  x[1..$-1]))
>                 .reduce!((string s, string x) =>  s ~= x)("BLAH");
> -----------------------------------------
>
> This could be fixed with a breaking change by making the subject range to
> be the first parameter. Aside from breaking existing code, are there
> other obstacles to changing this?
>
> Justin Whear

Yah, reduce was not designed for the future benefit of UFCS. (I recall 
take() was redefined towards that vision, and it was a good move.)

We can actually deprecate the current order and accept both by inserting 
the appropriate template constraints. We change the documentation and 
examples to reflect the new order, and we leave a note saying that the 
old order is deprecated. We can leave the deprecated version in place 
for a long time. Thoughts?


Andrei