[fpc-pascal] Fwd: What to do to get new users

[Nikolay Nikolov]

On 1/24/25 8:38 AM, Hairy Pixels via fpc-pascal wrote:
> On Jan 24, 2025 at 1:34:26 PM, Nikolay Nikolov via fpc-pascal 
> <fpc-pascal at lists.freepascal.org> wrote:
>> Doesn't matter whether they're handled in the same scope or not. It's 
>> the same code. Usually they're not handled in the same scope, but in 
>> a very distant place. That's usually when exceptions are convenient.
>> Once you let them bubble up you need to wrap all call sites with 
>> try..finally right?
>> Wrong. Only sites that allocate memory, that needs to be freed, 
>> before leaving the scope need a try..finally. You don't need to wrap 
>> every call. That's nonsense. The pattern is:
>>
>> var
>>
>>   {... initialize local vars you're going to allocate in this 
>> function with nil}
>>
>> begin
>>
>>   try
>>
>>     {lots of code, allocations, calls, etc}
>>
>>   finally
>>
>>     {cleanup code}
>>
>>     {free stuff that isn't nil}
>>
>>   end;
>>
>> end;
>>
>
> Yes that’s what I meant. If you don't know which calls could fail you 
> need to wrap all functions that allocate memory in try..finally. 
> That’s what the original post was commenting on, the need for some 
> other syntax which knows to free a variable if the function terminates 
> early due to an exception, like the implicit exception frames for 
> managed types like dynamic arrays.

Yes, that could probably save some typing, however it comes at a price:

1) only works for classes

2) not obvious order of destructor calls. What if they have side 
effects, and the order matters?

3) doesn't support procedural APIs.

In really, I find try..finally to be much nicer, because you can do a 
proper cleanup in the finally section that includes any of the following:

* destructor calls

* FreeMem

* Dispose

* function calls (e.g. Close(), XFree(), etc.)

And the order is well defined by you.

So, I prefer try..finally. And it's not much typing, when used properly.

Nikolay
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