Re: Move semantics

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 2022-09-20 14:44, AdaMagica wrote:
> Paul Rubin schrieb am Montag, 19. September 2022 um 20:50:50 UTC+2:
>> I think it refers to the C++ notion.
>> https://en.cppreference.com/w/cpp/utility/move
> 
> What I do not understand: Why should the move operation be less expensive than a copy?
> As I see it: First you have to do a copy, then delete the source.


The standard Ada containers have Move operations.

Containers are of course often implemented with indirection, where the 
container object contains accesses to the data held in the container, so 
a Move operation only has to copy the access values from the source to 
the target, and does not need to copy the data. The access values in the 
source are then nulled, making the source container empty. This is often 
less expensive than copying the data.

Eg. for Vectors, the Ada RM says "Move should not copy elements, and 
should minimize copying of internal data structures."

For the bounded Ada containers, which are not meant to use indirection, 
while there are Move operations the RM says that the implementation 
advice "to minimize copying" does not apply.