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From: John McCabe <JMcCabe@KT-LAP20-JM01.i-did-not-set--mail-host-address--so-tickle-me>
Newsgroups: comp.lang.ada
Subject: Re: Ada and "early return" - opinion/practice question
Date: Tue, 16 Mar 2021 11:51:51 +0000
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Stephen Leake <stephen_leake@stephe-leake.org> writes:

> John McCabe <"john@nospam.mccabe.org.uk"> writes:
>
>> On 15/03/2021 17:31, Stephen Leake wrote:
>>>John McCabe <john@mccabe.org.uk> writes:
>>>
>> <..snip..>
>>.. <..snip..>

>>>I would tend to use an exception for "something bad", but that depends
>>>on the overall design.

>> Thinking back on this point, would you do it a style where you try to do
>> what needs to be done then handle the exception when it fails? For example,
>> in this style
>>
>> begin
>>    <try to do a good thing>
>> exception
>>    when blah blah
>> end
>
> No, your example fn returns a status code to the caller for "something
> bad", so the Ada fn should raise an exception, and the caller (or some
> function up the call chain) should handle it.

>> Or do you mean, rather than return when the undesirable condition occurs, do
>> something like:

>> if <some undesirable condition 1> then
>>    raise <some exception 1>
>> end if;

> Yes, but with helpful info in the exception message:

>     raise <some exception 1> with "explanation";

That "with" part's new since I regularly used Ada :-)

> For example, if the problem is that some number is out of bounds, the
> "explanation" should include both the number and the bounds. And if the
> bounds can be adjusted by a user option, the option name.

That seems reasonable; similar to C++ where you can "throw
std::logic_error("message");" kind of thing.