sortOn: sorts range of aggregates by member name(s)

[Andrei Alexandrescu via Digitalmars-d]

On 11/5/14 12:18 PM, "Marc =?UTF-8?B?U2Now7x0eiI=?= <schuetzm at gmx.net>" 
wrote:
> On Wednesday, 5 November 2014 at 00:34:54 UTC, Meta wrote:
>> On Wednesday, 5 November 2014 at 00:32:32 UTC, Nordlöw wrote:
>>> Has there been any proposals to add a sort-wrapper, say sortBy,
>>>
>>> in cases such as
>>>
>>>    struct X { double x, y, z; }
>>>    auto r = new X[3];
>>>
>>> used as
>>>
>>>    r.sortBy!("x", "y")
>>>
>>> sorting r by value of "x" then "y".
>>>
>>> If not and anybody is interest I could write one and make PR in
>>> std.algorithm.
>>
>> I think you're looking for multiSort.
>>
>> http://dlang.org/phobos/std_algorithm.html#.multiSort
>
> That's not the same, it requires to specify a comparison function.
> Nordlöw wants to specify an attribute.
>
> This could also be an arbitrary expression, of course:
>
>      r.sortBy!"x*x + y*y + z*z"
>
> The above could be implemented using `with` and
> `std.functional.unaryFun`. Alternatively, a lambda could be used:
>
>      r.sortBy!(a => a.norm);

sortBy!(expr) is equivalent with sort!(expr_a < expr_b) so there's no 
additional power to it. However, it does make some sorting criteria 
easier to write. A while ago I took a related diff pretty far but in the 
end decided to discard it because it didn't add sufficient value.

Andrei