ruby syntactic sugar: dealing with nils

Question

probably asked already but I couldn't find it.. here are 2 common situation (for me while programming rails..) that are frustrating to write in ruby:

"a string".match(/abc(.+)abc/)[1]

in this case I get an error because the string doesn't match, therefore the [] operator is called upon nil. What I'd like to find is a nicer alternative to the following:

temp="a string".match(/abc(.+)abc/); temp.nil? ? nil : temp[1]

in brief, if it didn't match simply return nil without the error

The second situation is this one:

var = something.very.long.and.tedious.to.write
var = something.other if var.nil?

In this case I want to assign something to var only if it's not nil, in case it's nil I'll assign something.other..

Any suggestion? Thanks!

Answer 1

In Ruby on Rails you have the try method available on any Object. According to the API:

Invokes the method identified by the symbol method, passing it any arguments and/or the block specified, just like the regular Ruby Object#send does.

Unlike that method however, a NoMethodError exception will not be raised and nil will be returned instead, if the receiving object is a nil object or NilClass.

So for the first question you can do this:

"a string".match(/abc(.+)abc/).try(:[], 1)

And it will either give you [1] or nil without error.

Answer 2

Forget that Python atavism!

"a string"[/abc(.+)abc/,1] # => nil

Answer 3

"a string"[/abc(.+)abc/, 1]
# => nil
"abc123abc"[/abc(.+)abc/, 1]
# => "123"

And:

var = something.very.long.and.tedious.to.write || something.other

Please note that or has a different operator precedence than || and || should be preferred for this kind of usage. The or operator is for flow control usage, such as ARGV[0] or abort('Missing parameter').