On Mar 6, 2011, at 18:01, Anders Logg <l...@simula.no> wrote:
> On Sun, Mar 06, 2011 at 09:45:20PM +0000, Garth N. Wells wrote:
>>
>>
>> On 06/03/11 21:39, Anders Logg wrote:
>>> On Sun, Mar 06, 2011 at 10:29:10PM +0100, Marie E. Rognes wrote:
>>>> On 03/06/2011 10:22 PM, Anders Logg wrote:
>>>>> On Sun, Mar 06, 2011 at 09:08:10PM +0000, Garth N. Wells wrote:
>>>>>>
>>>>>>
>>>>>> On 06/03/11 21:02, Marie E. Rognes wrote:
>>>>>>> On 03/06/2011 09:30 PM, nore...@launchpad.net wrote:
>>>>>>>> if (parameters["max_dimension"].change_count()> 0
>>>>>>>> && V.dim()> max_dimension)
>>>>>>>> + {
>>>>>>>> return true;
>>>>>>>> -
>>>>>>>> - // Otherwise, not done.
>>>>>>>> - return false;
>>>>>>>> + }
>>>>>>>> + else
>>>>>>>> + return false;
>>>>>>>> }
>>>>>>>
>>>>>>>
>>>>>>> I notice that my early returns keep getting moved into else clauses... I
>>>>>>> find this approach less readable, especially when there are nested ifs.
>>>>>>> Why is it the preferred way?
>>>>>>>
>>>>>>
>>>>>> Because your comment basically says else, so I'd say it's better to have
>>>>>> the code say it consistently.
>>>>>>
>>>>>> I find it easier to follow, because it's clear that the function exits
>>>>>> from the conditional block. The return value is either true or false
>>>>>> depending on the one true/false evaluation.
>>>>
>>>>
>>>> The code is an if -- else if -- else. I don't see how moving that
>>>> into an if, if -- else increases consistency.
>>>>
>>>>
>>>>>
>>>>> I'm not sure we're talking about the same thing here, but I think the
>>>>> following examples are *good* practice:
>>>>>
>>>>> 1. Early return to get rid of special cases
>>>>>
>>>>> void foo()
>>>>> {
>>>>> // Get rid of some case
>>>>> if (...)
>>>>> return;
>>>>>
>>>>> // Get rid of another case
>>>>> if (...)
>>>>> return;
>>>>>
>>>>> // Do main bulk of work here
>>>>> ...
>>>>> }
>>>>>
>>>>> Alternative using if/else will force main code in one indentation
>>>>> level.
>>>>>
>>>>> 2. Fallback return at end of block
>>>>>
>>>>> bool foo()
>>>>> {
>>>>> // Handle case 1
>>>>> if (...)
>>>>> {
>>>>> ...
>>>>>
>>>>> return true;
>>>>> }
>>>>>
>>>>> // Handle case 2
>>>>> if (...)
>>>>> {
>>>>> ...
>>>>>
>>>>> return true;
>>>>> }
>>>>>
>>>>> // No foos found
>>>>> return false;
>>>>> }
>>>>
>>>>
>>>> Yep, I prefer 2. to an if -- else if (-- else if) -- else.
>>>
>>> It's also logical since the 'else' has no effect. So the policy can be
>>> to remove code that has zero effect.
>>>
>>
>> If it's a straight if - else, I have a pretty strong view that 'else'
>> should be used. C/C++ don't provide 'else' for nothing.
>
> 'else' does have an effect when there is no return inside the 'if'.
>
> This works:
>
> int a = 1;
> if (...)
> a += 1;
> else
> a += 2;
>
> This doesn't work:
>
> int a = 1;
> if (...)
> a += 1;
> a += 2;
>
> But consider this:
>
> if (...)
> return 1;
> else // this line can be remove and has absolutely no effect
> return 2;
>
>> Related, one strict school of thought says that both 1. and 2. are bad
>> since a function should only have one exit. We have had memory leaks
>> because of premature exits.
>
> I don't think that's a good policy. It would increase the number of
> indentations in general.
I can not find it right now but I have seen the example that Marie presented as
"good programing practice" for C\C++ because of the simple reason which both
Marie and Anders advocate: simpler code cause less mistakes.
I also think "else is there for a reason" is a silly argument.
Johan
> --
> Anders
>
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