From: Robert Klemme <bob.news@...>
Date: 2004-06-13T04:43:37+09:00
Subject: Re: assignment in conditional warning


"Ara.T.Howard" <ahoward@noaa.gov> schrieb im Newsbeitrag
news:Pine.LNX.4.60.0406120931350.3345@harp.ngdc.noaa.gov...
> On Sat, 12 Jun 2004, Robert Klemme wrote:
>
> >> Most novice programmers would want to use that.
> >
> > I beg to differ: the *only* reasonable usage of assignment in
conditionals
> > is with "while" and "until", i.e. looping constructs, like in:
> >
> > while ( line = gets )
> >  line.chomp!
> >  # do something with current line
> > end
> >
> > Assignment in "if" and "unless" is totally superfluous.  It obfuscates
code
> > and is not needed at all.  Every "if ( x = expression )" can be
converted to
> >
> > x = expression
> > if x
> > ...
> >
> > which is *much* clearer and cleaner IMHO.  Alternatively you can do this
in
> > some cases:
> >
> > x = expression and puts "yes"
>
> IMHO the above fails apart when you are testing compound datastructures
using
> assignment to deconstruct the structure into more manageable peices in the
> test.  which is cleaner/clearer?
>
> 1)
>
>    tuples = db.execute sql
>
>    raise "something terrible has happened in the database" unless
>      (tuple = tuples.first) and (answer = tuple.first) and (answer == 42)
>
> 2)
>
>    tuples = db.execute sql
>
>    raise "something terrible has happened in the database" unless
>      tuples.first and tuples.first.first and tuples.first.first == 42
>
> 3)
>
>    tuples = db.execute sql
>
>    tuple = tuples.first
>    answer = tuple.first
>
>    raise "something terrible has happened in the database" unless
>      answer == 42
>
>
>
> i can seem someone chosing 1 or 3 from above.  but when the code size
starts
> to grow i think most programmers, given a choice between two clear
statements,
> chose the shorter one and that, in fact, the __length__ of a statement
> relative to it's source file is directly related to it's
understand-ability.
> especially consider the case where the variables 'tuple' and 'answer' are
not
> used except for testing purposes - isn't it better to isolate them to the
> conditional expression then?  if course, you don't have to name them at
all
> (2), but that IS obfuscated!

One of the three tests is superfluous.  So it's rather

tuples = db.execute sql
raise "something terrible has happened in the database" unless
    tuples.first && tuples.first.first == 42

which doesn't look too bad IMHO.

Regards

    robert