What does the ~> symbol mean in a bundler Gemfile?

问题:

My question is pretty much in the title.

e.g. in the default Gemfile created with a Rails 3.1 app;

gem 'sass-rails',   '~> 3.1.5'

It seems like I should know this already but I can't find any reference to it on the Bundler website.

回答1:

From the bundler website:

The specifier ~> has a special meaning, best shown by example. ~> 2.0.3 is identical to >= 2.0.3 and < 2.1. ~> 2.1 is identical to >= 2.1 and < 3.0. ~> 2.2.beta will match prerelease versions like 2.2.beta.12.

See http://gembundler.com/gemfile.html and http://guides.rubygems.org/patterns/#pessimistic-version-constraint

回答2:

You usually use this to tell bundler that it's ok to install some minor updates (last digit specified can vary) but not to install some major update.

SO

~> 2.0.3 means >= 2.0.3 ∩ < 2.1

and

~> 2.1 means >= 2.1 ∩ < 3.0

Read more at http://gembundler.com/gemfile.html