[fpc-devel] Minor doc error about "const param"

Martin Frb lazarus at mfriebe.de
Mon Dec 20 13:11:26 CET 2021

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 
But insert a call to a subroutine doing the work, or start a thread....

procedure foo(const t: AnsiString);
   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....

   GlobalTxt: AnsiString;

   GlobalTxt := getRandomTextWichIsNotAConstant;

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