问题
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!
回答1:
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
回答2:
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.
回答3:
Forget that Python atavism!
"a string"[/abc(.+)abc/,1] # => nil
回答4:
"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').
回答5:
"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
回答6:
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}
来源：https://stackoverflow.com/questions/4565496/ruby-syntactic-sugar-dealing-with-nils