On 05/01/2025 07:15, Hairy Pixels via fpc-pascal wrote:
On Jan 5, 2025 at 11:53:36 AM, Adriaan van Os via fpc-pascal
<fpc-pascal@lists.freepascal.org
<mailto:fpc-pascal@lists.freepascal.org>> wrote:
This is a habit from the WIndows and Delphi world. In a one-levell
namespace on MacOS, the dll name
is superflouous. Note that ObjC symbols are always global ,which
implies a one-level namespace.
what do you mean a one level namespace?
I thought the idea of external names is that you could resolve name
conflicts. Like if you had “exit” declared in 2 libraries can they both
be linked together in one program using the external name? I’m curious
about this though because I’ve never seen a way to do that with a
linker, all you can ever do is specify libraries then the linker does
all the work and if there are duplicates you get an error, end of story.
That is exactly what namespaces mean.
On Windows, every DLL has its own namespace. I.o.w., the external
symbol's mangled name is in part determined by the DLL it gets imported
from, and in part by the symbol name itself.
Most Unix platforms use a single-level namespace, where the name of the
library is irrelevant and all external symbols' names only depend on the
symbol name. If multiple libraries export the same symbol, generally the
one of the last one loaded gets used (when manually looking up a symbol
address at run time, you have more options). Of course, programming
language themselves can still use namespaces themselves (e.g. Pascal
units and C++ namespaces).
That said, Darwin also uses two-level namespaces:
https://blog.darlinghq.org/2018/07/mach-o-linking-and-loading-tricks.html#two-level-symbol-namespace
. However, it does not do this through name mangling. The linker simply
encodes in the generated binary in which library/framework it found the
symbol at link time. Then, at run time, the dynamic linker will only
look for that symbol in that specific library (unless you force a
flat/single namespace through an environment variable).
However, as Adriaan also mentioned, an exception to this is Objective-C,
which has its own name-based resolution logic. And having the same
Objective-C class defined in multiple files, or having multiple
categories adding the same method to the same class, will result in a
random one getting picked at run time. And that results in real-world
problems:
https://steamcommunity.com/app/335620/eventcomments/4843147760499908525?snr=1_2108_9__2107&ctp=2#c4840896974229538203
Jonas
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