Why exceptions for error handling is so important

[via Digitalmars-d]

On Tuesday, 13 January 2015 at 23:58:53 UTC, deadalnix wrote:
>
> http://dlang.org/phobos/core_thread.html#.Thread.join

I don't see the problem. I'm suggesting value semantics, it can 
be copied.

> When you are in the catch, you are not unwinding anymore. You 
> could indeed loose chaining to be able to reuse the memory, 
> that is not what is slow when it come to exception, so it won't 
> make it fast.

You can't have chaining with this scheme...? But since you can 
only have one instance it has to be initialized with value 
semantics. It's a small constraint.

Not using regular Itanium-style unwinding will make it 
potentially faster. Using TLS makes it possible to propagate over 
non-D code or code where the register pressure is high, it can be 
optimized away so you don't need TLS if you don't span over non-D 
code.

>> 1. So that you can mark a non-D function with @checkexception 
>> and allow it to both cast D-exceptions and propagate 
>> D-exceptions.
>>
>
> Empty hand waving, not not addressing the point.

Who are you waving at?

Non D functions can cast by setting the TLS memory to an 
exception value, then do a regular return. The D function that 
called the non-D function will check TLS memory to see if there 
is an exception in flight.

>>> Skipping 4 and 5, you obviously didn't though that through.
>>
>> ?
>
> What you propose in point 1 - 3 is weak at best. You haven't 
> put serious effort thinking about what you are proposing, so 
> there is no reason anyone should spend any serious effort 
> criticizing it.

Then don't bother.

If your point regarding point 4 was that it would limit cross 
compiler linking, then yes. And that would be intentional, since 
it is far too soon to standardize D at that level. It just 
prevents experimentation and performance gains.

If your point regarding point 5 is that it would be too limiting, 
well then you would need to differentiate between D and C 
entrypoints to D functions to overcome the problem. That's 
possible, but IMO not worth it.