[fpc-devel] Question on constref

[Michael Van Canneyt]

On Thu, 2 Feb 2023, Hairy Pixels via fpc-devel wrote:

>
>
>> On Feb 2, 2023, at 3:57 PM, Adriaan van Os via fpc-devel <fpc-devel at lists.freepascal.org> wrote:
>> 
>> - under what circumstances (and in what compiler mode) does FPC pass large (say 1 MB or 1 GB) "const" parameters by value (which is extremely inefficient) ?
>> - for what reasons ?
>> 
>> As long as these questions are not addressed and cleared and documented "const" parameters are not a useable in actual code.
>
> That’s what I want to know.  There should be a hard rule like records over
> X bytes are passed by reference.  In the issue you posted they said they
> had a massive performance penalty in their library because const was
> passing by value and this makes people like myself paranoid so I’m
> inclined to use constref everywhere with larger records.

It depends on the platform ABI, and hence we don't document it.

I don't see your problem, to be honest:

You want to indicate a parameter to a function cannot be changed in its implementation.

If you don't care about how it is passed, use const.

If really want a reference to be passed for performance or other reasons, use constref.

So you're doing the right thing by using constref.

Couldn't be simpler.

Michael.