On Mon, 20 Dec 2021, Martin Frb via fpc-devel wrote:
On 20/12/2021 12:29, Michael Van Canneyt wrote:
On Mon, 20 Dec 2021, Martin Frb via fpc-devel wrote:
Actually an commission, but an important one.
https://www.freepascal.org/docs-html/current/ref/refsu67.html#x183-20700014.4.4
> Specifying a parameter as Constant is giving the compiler a hint
that the contents of the parameter will not be changed by the called
routine.
"by the called routine."
Should that not be "by any code (the caller, the called, or any
nested callee, or any other thread, interrupt or hardware modifying
memory)"?
If the value is copied then nothing else can change it since it is only
accessible to the routine itself ? (unless you're doing some really dirty
tricks, obviously)
In the below example "GlobalTxt := 'abc';" is indeed in the "called
routine".
But insert a call to a subroutine doing the work, or start a thread....
procedure foo(const t: AnsiString);
begin
GlobalTxt := 'abc';
// do some mem alloc/dealloc work
// do something with t, it still points to the location that the old
content was in. If that mem has been changed....
Well, that's what I meant with really dirty tricks.
I will probably have to rephrase the documentation to
'The compiler will not allow you to modify the parameter value by assigning something directly to it."
Michael.
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