copying memory in phobos

[monarch_dodra]

On Wednesday, 9 April 2014 at 08:24:55 UTC, Mike wrote:
> On Tuesday, 8 April 2014 at 14:59:35 UTC, Artur Skawina wrote:
>> 'memcoy' being a built-in compiler intrinsic means that when 
>> the compiler
>> sees a 'memcpy' call, it does some checks (eg is the length 
>> statically
>> known and small enough?) and then can generated the copy 
>> instructions
>> directly, instead of calling the lib function.
>
> Then it could do such magic in the _d_arraycopy function where 
> the call to memcpy exists.  I'm still not seeing the motivation 
> behind putting this call to memcpy in Phobos.

Depending on the type being copied, "a[] = b[]" is not straight 
up "memory copy" it's the actual full assignment, with postblit 
and all. That's why the call we want is *really* memcpy.

The code where you saw this, if I'm not mistaken, is 
"inPlaceInsert" or something of the like. The idea in this code 
is to actually *move* the data, not create *copies* elsewhere.

The array assign is a fallback for CTFE. It's fine in CTFE, 
because we don't care about performance, but it's not the actual 
call we want.