core.stdc.stdlib._compare_fp_t and qsort

[Dmitry Olshansky]

On Sunday, 18 March 2018 at 11:29:47 UTC, Joe wrote:
> On Monday, 12 March 2018 at 03:50:42 UTC, Joe wrote:
>> On Monday, 12 March 2018 at 03:13:08 UTC, Seb wrote:
>>> Out of interest: I wonder what's your usecase for using 
>>> qsort. Or in other words: why you can't use the high-level 
>>> std.algorithm.sorting.sort?
>>
>> This is only temporary. I will be using 
>> std.algorithm.sorting.sort. I was converting a C program and 
>> it annoyed me that I couldn't get the qsort invocation past 
>> the D compiler.
>
> Now that I'm trying to use std.algorithm.sorting, I'm again 
> puzzled by what I need to use for the "less" predicate. My 
> first try was:
>
>    sort!((a, b) => to!string((*a).name) < 
> to!string((*b).name))(recs);
>
> This results in the error:
>
> Error: template std.algorithm.sorting.sort cannot deduce 
> function from argument types !((a, b) => to!string((*a).name) < 
> to!string((*b).name))(Record*[10]),

This basically says you have fixed size array, in D they don’t 
decay to slices/pointers for safety reasons (it’s stack memory 
that is easy to leak out of scope with disasterous consequences).

Do this to get the usual ptr + length:

sort!((a, b) => to!string((*a).name) < 
to!string((*b).name))(recs[]);

Also to!string would be computed on each compare anew. May want 
to use schwartzSort to avoid that, on 10 elements there is no 
real difference though.