红宝石中关键字“do”的含义是什么？

Question

I've seen a couple of do in Ruby, and I couldn't find a really good explanation of its purpose. For example, a place where I saw a do was in the gemfile :

group :development, :test do
    gem 'rspec-rails'
    gem 'rspec-its'
    gem 'simplecov', :require => false
    gem 'guard-rspec'
    gem 'spork-rails'
    gem 'guard-spork'
    gem 'childprosess'
    gem 'rails-erd'
    gem 'pry-rails'
    gem 'guard-rails'
    gem 'guard-livereload'
    gem 'guard-bundler'
end

I know what this code does, but I don't know the purpose of do . I have my guesses, but I want them confirmed or denied by someone who knows more than me.

Answer 1

do ... end (or alternatively { ... } ) creates a so-called block, which is a type of anonymous function in Ruby. In your example that block is passed as an argument to group . group then does some bookkeeping to set the given groups as active, executes the block, and then deactivates the groups again.

Answer 2

The do keyword is used together with the end keyword to delimit a code block.

More info on the difference of do end with brackets may be found here: http://ruby-doc.org/docs/keywords/1.9/files/keywords_rb.html#M000015

Answer 3

It is a block In other programming languages you using brackets, like this: {} . In ruby you can use:

do

  #something code

end