Things C++ 20 Deliberately Broke

[Siarhei Siamashka]

On Wednesday, 28 September 2022 at 19:43:34 UTC, German Diago 
wrote:
> On Monday, 26 September 2022 at 08:32:27 UTC, Siarhei Siamashka 
> wrote:
>> On Monday, 26 September 2022 at 03:24:57 UTC, norm wrote:
>
>> If Python developers decided to keep both Python2 and Python3
>> maintained forever, then it would be similar to C++ and Rust.
>
> Not at all. Python 2/3 is a split with incompatibilities.

These were not fatal incompatibilities though. Single-source 
Python 2/3 compatible code used to be a thing:

* https://docs.python.org/3/howto/pyporting.html
* https://python-future.org/compatible_idioms.html

Of course having two slightly incompatible variants of the 
programming language is not ideal. That's surely some extra work 
for compiler/interpreter developers and also extra work for 
popular libraries developers. But application developers didn't 
have any urgency to waste resources on migrating their existing 
Python2 code to Python3 and instead could focus on delivering 
amazing features to their users.

Is the convenience of 1 compiler developer or the convenience of 
1000 application developers more important for a programming 
language? The answer depends on many factors. And the size of the 
existing ecosystem is one of them.

> C++ is a deprecation + removal model except for very, very few 
> exceptions. You can compile C++98 code in a C++20 compiler 
> almost without any change.

You can surely compile a simplistic C++98 helloworld code by a 
C++20 compiler with no changes at all. But Chromium developers 
couldn't easily compile their C++17 code by a C++20 compiler. 
That's exactly what this forum thread is all about. The key 
difference is that Chromium is a huge project.

C++ language has multiple supported versions of the language 
standard for a reason and this is a lifesaver for the projects 
with huge codebases, which have to be maintained over the span of 
many years or decades. If C++ compilers decided to drop support 
for the older versions of the language standard, then this would 
be similar to what Python did.