On 2024-03-18 13:29, Hairy Pixels via fpc-pascal wrote:
On Mar 18, 2024, at 5:29 PM, Michael Van Canneyt via fpc-pascal
<fpc-pascal@lists.freepascal.org> wrote:
Of course there must be, that's the whole point of copy-on-write.
As soon as one reference is changed, a copy is made if the reference
count
is larget than 1, and this copy is changed.
Oh, it does copy on write. I see now that by looking at the pointer
addresses.
So what happens if you do this? s2 is pointing to s1 but then you
change the size of s1 and ReAllocMem gets called and invalidates the
pointer to the original s1. How does s2 know this and not access
corrupted memory now?
s1 := '123';
s2 := s1;
s1 := 'xxxxxxxxxxxx';
From user point of view, the result is the same as when s1 and s2 are
declared as shortstring (i.e. s2 = '123' and s1 = 'xxxxxxxxxxxxx'). From
technical point of view, the original location is used for s2 (with
reference count 1), whereas s1 points to a new location (with reference
count also 1 at that point in time).
Tomas
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