Templates: Array slices not recognized

[Chris via Digitalmars-d-learn]

On Monday, 20 April 2015 at 09:58:06 UTC, Marc Schütz wrote:
> On Monday, 20 April 2015 at 09:07:54 UTC, Chris wrote:
>> On Saturday, 18 April 2015 at 17:59:19 UTC, ketmar wrote:
>>> On Sat, 18 Apr 2015 17:50:56 +0000, Chris wrote:
>>>
>>>> Doh! You're right! My bad. However, this makes the function 
>>>> less
>>>> generic, but it doesn't matter here.
>>>
>>> maybe `auto ref` can help here?
>>
>> Yes, auto ref does the trick. I prefer it to passing the slice 
>> by value, because I can extend the function to cater for more 
>> types. My implementation (which is different from the one 
>> posted above) works also with strings, for example. Anyway, it 
>> gave me a performance boost of ~2.7 times as compared to the 
>> workarounds I had. This was well worth it!
>
> Strings are slices, too. `string` is equivalent to 
> `immutable(char)[]`.

I know. My function returns an array of the same type (size_t[] 
or a string (immutable(char)[] or whatever). With auto ref I can 
pass a string without having to slice it, like so

string a = "bla";
string b = "blub";

auto res = doSomething(a, b);

If I didn't use "auto ref" or "ref", string would get copied, 
wouldn't it?

auto ref doSomething(R needle, R haystack);

To avoid this, I would have to write a[0..$], b[0..$], which is 
not nice. Right or wrong?

For the record, I put the function inside a struct which again 
boosted the performance. No it is faster by a factor of ~3.17. 
Using the struct is even slightly faster than executing the same 
code directly within the for loop. That surprised me.