[fpc-devel] Question on constref

[Sven Barth]

Am 01.02.2023 um 11:30 schrieb Bart via fpc-devel:
> I thought that constref would be OK for that (the word constref
> suggests to me tah the paramter will be treated (by me) to be a
> constant, and that it shall be passed by reference in all cases,
> whereas with a const parameter the compiler decides upon the best way
> to pass it: by value or by reference).
> I tried to find documentation for constref, but all I could find was:
> https://wiki.freepascal.org/FPC_New_Features_2.6.0#Constref_parameter_modifier
> There it says:
> "Note that in general, it should only be used for interfacing with
> external code or when writing assembler routines."

“constref” is guaranteed to pass the parameter by reference. And the 
compiler will ensure that it can't be modified as reasonably possible 
(as with “const” there are ways to circumvent this, e.g. by passing 
around a pointer to the parameter, but the general cases are covered).
> (B.t.w.: Where can I find the official documentation on constref?)

There is no full documentation for that parameter modifier (someone 
might want to file a bug report for that), but the documentation for 
“const” ( 
https://www.freepascal.org/docs-html/current/ref/refsu67.html#x183-20700014.4.4 
) contains this:

=== doc begin ===

Contrary to Delphi, no assumptions should be made about how const 
parameters are passed to the underlying routine. In particular, the 
assumption that parameters with large size are passed by reference is 
not correct. For this the constref parameter type should be used, which 
is available as of version 2.5.1 of the compiler.

=== doc end ===

Regards,
Sven
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