CODEWITHSUNDEEP
rubyidioms
luca
luca

Reputation: 12601

ruby syntactic sugar: dealing with nils

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!

Upvotes: 5

Views: 581

Answers (6)

sawa
sawa

Reputation: 168121

For the first question, I think Bob's answer is good.

For the second question,

var = something.very.long.and.tedious.to.write.instance_eval{nil? ? something.other : self}

Upvotes: 0

Bob Aman
Bob Aman

Reputation: 33239

"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').

Upvotes: 3

Nakilon
Nakilon

Reputation: 35084

Forget that Python atavism!

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

Upvotes: 3

Phrogz
Phrogz

Reputation: 303261

"a string".match(/foo(bar)/).to_a[1]

NilClass#to_a returns an empty array, and indexing outside of it gives you nil values.

Alternatively (what I do) you can splat the matches:

_, some, more = "a string".match(/foo(bar)(jim)/).to_a

Upvotes: 0

icecream
icecream

Reputation: 1425

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.

Upvotes: 2

tokland
tokland

Reputation: 67880

For the first I'd recommend ick's maybe (equivalent to andand)

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

I am not sure I understand the second one, you want this?

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

Upvotes: 0

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