Re: Re: Why is 'else' demanded?

I've known what you mean. ' UNLESS it contains a return statement, as there=
turn now goes to another end.' =0D
The sentence tells me why the IDE I use doesn't support the refactor a seri=
es statements including return in =0D
a function.=0D
' Once the if statement has run, the situation might have changed.' I never=
 use try catch statements to do the job=0D
like you describe, so I don't know the ifs' use in the condition.=0D
Maybe 'it is a matter of style', the freedom of a programmer is important.=
=0D
=0D
Thank your answers.=0D
=0D
Best regards,=0D
ZhangHong-liang=0D
=0D
=0D
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=85=AC=E5=8F=B8 (ShangHai Raxtone Limited Company)=0D
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=8E=A7=E8=82=A1=E5=A4=A7=E5=8E=A6201=E5=AE=A4 (Room 201, Buliding HuaYi con=
trol, No.11, CaiHeFang Road, Beijing , China)=0D
Fax:82870098=0D
=0D
=0D
From: Willem Bogaerts=0D
Date: 2013-06-10 17:41=0D
To: refactoring=0D
Subject: Re: [refactoring] Why is 'else' demanded?=0D
  =0D
=0D
> I have a problem. Why is there always else key word in a language?=0D
> Since I can use return to stop the process of a flow. I hate to see=0D
> else statement and I see I can never use else statement that only=0D
> increase the complexity of program.=0D
=0D
I would turn it the other way around: Why is there a return statement in=0D
most languages? "return" in those languages means "go to end" and is the=0D
one "go to" statement that keeps standing in the way of refactoring.=0D
=0D
For example, you can take any code out of a function that has the same=0D
structural level (like the inner part of a while loop) and extract it=0D
into a function or method, UNLESS it contains a return statement, as the=0D
return now goes to another end.=0D
=0D
In other words: refactoring starts with "structured programming" (the=0D
paradigm shift in the 1980s where "if - go to" statements were replaced=0D
by "while", "repeat" and "if-then-else" statements in a lot of=0D
languages). The return statement is not part of a structured program. (I=0D
know, if you use the return statement as the last statement in a=0D
function you have effectively worked around the "go to" part and you=0D
usually have no choice if you need the return statement to pass the=0D
return value.)=0D
=0D
> A if statement stands for a condition that should be unique, and it=0D
> should has no relation with anything else. So a language does not=0D
> need else and it should not appear in a program.=0D
=0D
But "if" is never unique, nor is that a demand. For example, my code=0D
sometimes feature the same if statement a few times, because the inner=0D
part of a previous if statement has "refreshed" the condition. For example:=
=0D
=0D
SomeObject =3D null;=0D
... try to get SomeObject from application cache ...=0D
if SomeObject is null:=0D
... read the object from the session cache ...=0D
endif;=0D
if SomeObject is null:=0D
... create a new one from database data...=0D
endif;=0D
=0D
The same thing is true for an "else" condition. Once the if statement=0D
has run, the situation might have changed. The use of an "else" keyword=0D
is than an elegant way to describe that the code should not re-evaluate=0D
the condition.=0D
=0D
Apart from that, it is a matter of style. For example, Python has the=0D
phrase "It is easier to ask forgiveness than permission" and does a lot=0D
in try/catch statements ("asking forgiveness") where others would have=0D
used if statements ("asking permission"). It depends on your code (and=0D
your taste) which of the forms is more descriptive.=0D
=0D
Best regards,=0D
=0D
Willem Bogaerts.=0D
=0D


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