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

This question already has answers here: Meaning of tilde-greater-than (~>) in version requirement? (4 answers) Closed 8 years ago.

What does ~> mean in the context of Ruby gem depenedencies?

For example, when opening a legacy project in the RubyMine IDE, I get this message

Gems required for project are not attached:
arel (~> 2.0.2),
rspec-expectation (~> 2.5.0)...

I've seen this tilde-greater-than notation elsewhere in the Ruby world开发者_StackOverflow (it's not specific to RubyMine). Does this operator have a name other than the awkward-sounding tilde-greater-than?

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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

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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.?

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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.

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What this means is that you are expecting a gem that is version 2.0.2 or higher, but not 2.1 in the case of arel (~> 2.0.2) This is done since people are not supposed to release breaking syntax changes in minor revisions. So arel 2.0.3 would be expected to have bug/stability fixes over 2.0.2