What does tilde-greater-than (~>) mean in Ruby gem dependencies?

According to the internet

If a RubyGem dependency uses the syntax "~> 1.4.37", that means "a version greater than or equal to 1.4.37, but not 1.5 or higher." 1

In other words, for you
arel can be 2.1 > version >= 2.0.2 and
rspec-expectation can be 2.6 > version >= 2.5.0.

it means bring any lower version equal or greater than, but not a major version.

So for example arel (~> 2.0.2), will use (if availble) versions

• 2.0.2
• 2.0.3
• 2.0.? (as long as ? is >= 2)

but it won't use 2.1.?

It means "equal to or greater than in the last digit", so e.g. ~> 2.3 means "equal to 2.3 or greater than 2.3, but less than 3.0", while ~> 2.3.0 would mean "equal to 2.3.0 or greater than 2.3.0, but less than 2.4.0".

You can pronounce it as "approximately greater than".

§ Pessimistic version constraint