And Begin Idiom to avoid if with assignments

and_begin_idiom.rb

# After reading this comment
# http://avdi.org/devblog/2010/08/02/using-and-and-or-in-ruby/#comment-1098 ,
#
# I became aware of a cool idiom for Ruby.
#
# I've seen this in a lot of cases:

if (variable = expression_or_method(options))
  variable.calculate_something
  do_other_stuff(variable)
end

# This is another way to code the same concept:

variable = expression_or_method(options) and begin
  variable.calculate_something
  do_other_stuff(variable)
end

# The former case issues a warning because we're using = in an if statement.
# The latter seems more semantic to me too.
# What do you think??? Comments below!

Is there any difference when using and or && in this case? Haven't tried it but I'm assuming that if the expression_or_method returns false or nil then the rest will be shortcircuited and not bypassed.

@mclosson: I guess you're right, seems safer to me if expression_or_method returns nil

I liked this idiom, the resulting code is much cleaner.

@mclosson

if we had used && instead of and, the block would be evaluated and it would be like:
variable = ( expression_or_method(options) && something_the_block_returns )

This is not what we wanted to achieve. In our case, and using &&, it would be like:
(variable = expression_or_method(options) ) && something_the_block_returns

nice catch, george! 'and' and '&&' have differente precedences.

'&&' has a different precedence than 'and'

Here is a nice example of what George just explained:
http://blog.jayfields.com/2007/08/ruby-operator-precedence-of-and-which.html

I liked this idiom as well, specially the examples in the post linked at the top, from where this discussion started.

I use and prefer the first one. In my opinion the second options is more difficult to read.

I prefer the first one too, for me it's kind of weird to have a begin block after a assignment when reading the code. But I'm not against.

I agree with Urubatan about the first but I prefer the third alternative described by the author of that comment.

variable = expression()
if variable
do_stuff_with(variable)
end

Cheers =]

The first one is easier to read and understand I think.

The fact that #2 relies on the precedence of 'and' seems a good reason not to use it. I much prefer #1.

I've added another alternative using unless, though I still prefer #1

haven't seen this much either. aesthetically to me doesn't appeal more than the if example.

We do use a similar idiom on our project for doing simple multiline memoization on some methods like this excerpt: http://gist.github.com/561113

and the only reason why 'and' even exists in ruby is the fact that it has a different precedence to '&&', so I don't think its a good reason not to use it, unless you want to argue using 'and' is never a good idea.

I prefer the first case. Like hugobarauna said.

Pretty good. Both have use cases depending on the situation.

cool

I'll go with assignment then checking.

variable = expression(something)
if variable
end

Can't be easier to read than that.

While the 2nd syntax is new to me and sounds "Techy" - I would still take the simple approach of assigning first and then checking. It way more readable to me this way.

Heavily dislike the 2nd syntax. It's extremely clever and hard to read. You should be asking yourself: Will the next person to read this code have a clear idea what I've done? I can't see yes being the answer.

Thinking in that way I agree with @evanphx. Second syntax is not common and most of people we don't know how it works.

i prefer the if, by far.

In the second, there seems to be a condition

Typically, when I'm doing something like this, I want to be able to specify an elsif or else condition, which isn't possible using begin, for instance:

if rubygem = Rubygem.find_by_name(gem_name)
  render :json => rubygem.public_versions
else
  render :text => "This rubygem could not be found.", :status => 404
end