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A pattern is an object that wraps a Ruby pattern matching expression. The expression would normally be passed to an ‘in` clause within a `case` expression or a rightward assignment expression. For example, in the following snippet:
case node in ConstantPathNode[ConstantReadNode[name: :Prism], ConstantReadNode[name: :Pattern]] end
the pattern is the ConstantPathNode[...] expression.
The pattern gets compiled into an object that responds to call by running the compile method. This method itself will run back through Prism to parse the expression into a tree, then walk the tree to generate the necessary callable objects. For example, if you wanted to compile the expression above into a callable, you would:
callable = Prism::Pattern.new("ConstantPathNode[ConstantReadNode[name: :Prism], ConstantReadNode[name: :Pattern]]").compile callable.call(node)
The callable object returned by compile is guaranteed to respond to call with a single argument, which is the node to match against. It also is guaranteed to respond to ===, which means it itself can be used in a ‘case` expression, as in:
case node when callable end
If the query given to the initializer cannot be compiled into a valid matcher (either because of a syntax error or because it is using syntax we do not yet support) then a Prism::Pattern::CompilationError will be raised.
TruffleRuby >= 24 defines REUSE_AS_BINARY_ON_TRUFFLERUBY in defaults/truffleruby. However, TruffleRuby < 24 defines REUSE_AS_BINARY_ON_TRUFFLERUBY directly in its copy of lib/rubygems/platform.rb, so it is not defined if RubyGems is updated (gem update –system). Instead, we define it here in that case, similar to bundler/lib/bundler/rubygems_ext.rb. We must define it here and not in platform.rb because platform.rb is loaded before defaults/truffleruby.
Available list of platforms for targeting Gem installations.
See ‘gem help platform` for information on platform matching.
BasicSpecification is an abstract class which implements some common code used by both Specification and StubSpecification.
Base class for all Gem commands. When creating a new gem command, define initialize, execute, arguments, defaults_str, description and usage (as appropriate). See the above mentioned methods for details.
A very good example to look at is Gem::Commands::ContentsCommand