do..end vs curly braces for blocks in Ruby

Question

I have a coworker who is actively trying to convince me that I should not use do..end and instead use curly braces for defining multiline blocks in Ruby.

I'm firmly in the camp of only using curly braces for short one-liners and do..end for everything else. But I thought I would reach out to the greater community to get some resolution.

So which is it, and why? (Example of some shoulda code)

context do
  setup { do_some_setup() }
  should "do somthing" do
    # some more code...
  end
end

or

context {
  setup { do_some_setup() }
  should("do somthing") {
    # some more code...
  }
}

Personally, just looking at the above answers the question for me, but I wanted to open this up to the greater community.

Answer 1

The general convention is to use do..end for multi-line blocks and curly braces for single line blocks, but there is also a difference between the two that can be illustrated with this example:

puts [1,2,3].map{ |k| k+1 }
2
3
4
=> nil
puts [1,2,3].map do |k| k+1; end
#<Enumerator:0x0000010a06d140>
=> nil

This means that {} has a higher precedence than do..end, so keep that in mind when deciding what you want to use.

One more example to keep in mind while you develop your preferences.

The following code:

task :rake => pre_rake_task do
  something
end

really means:

task(:rake => pre_rake_task){ something }

And this code:

task :rake => pre_rake_task {
  something
}

really means:

task :rake => (pre_rake_task { something })

So to get the actual definition that you want, with curly braces, you must do:

task(:rake => pre_rake_task) {
  something
}

Maybe using braces for parameters is something you want to do anyways, but if you don't it's probably best to use do..end in these cases to avoid this confusion.