On Thu, 2 Feb 2023, Ondrej Pokorny via fpc-devel wrote:
On 02.02.2023 07:42, Sven Barth via fpc-devel wrote:
The case when you *need* a constant reference. Case in point: the
passing of TGuid in IInterface.QueryInterface. Delphi code relies on
it being a reference, but “const” does not guarantee that for all
platforms.
Maybe I am missing something, could you please explain why
IInterface.QueryInterface needs constref?
IIRC Joost introduced it at some point, but I don't remember exactly why.
I seem to remember constref was introduced as the equivalent of const *
parameters in C.
It allows to skip the pointer.
function TObject.GetInterface(const iid : tguid;out obj) : boolean;
that has a const without ref.
---
I myself cannot think of any real use case of constref other than hacks
like the FreeAndNil in recent Delphi versions:
procedure FreeAndNil(const [ref] Obj: TObject);
that needs the ref because it changes it to nil (so is not really a
const - it used to be an untyped var). As a result FreeAndNil allows you
to happily pass read-only properties to it that are then nilled.
Which is a clear violation of the concept of Const... :/
Michael.
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