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Seiei Miyagi
Seiei Miyagi

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How to define the method for the DSL configuration file

#ruby #rake

You can define the method for the DSL configuration file1 by Refinements.

For example, the hi method in a following code can use only in this Rakefile, it shouldn't affect any code outside of the Rakefile.

# Rakefile main = self using Module.new { refine(main.singleton_class) do def hi puts :hi end end } desc 'hi' task :hi do hi end
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% rake hi hi
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Common mistake 1

The following code defines the method at top level.

# Rakefile def hi puts :hi end desc 'hi' task :hi do hi end
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Common mistake 2

The following code defines the method at top level.

# Rakefile desc 'hi' task :hi do def hi puts :hi end hi end
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Common mistake 3

The following code defines the method at top level.

 # Rakefile m = Module.new do def hi puts :hi end end desc 'hi' task :hi do include m hi end
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Why should we avoid to define the method at top level?

It possibly breaks other libraries code.

For example:

# duck.rb class Duck < Struct.new(:name) def sound puts 'quack' end end
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# Rakefile require_relative 'duck.rb' def puts(*) print 'Hi! ' super end desc 'hi' task :hi do duck = Duck.new('Donald') puts duck.name duck.sound end
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$ rake hi Hi! Donald Hi! quack
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The benefit of the Refinements

The ruby's Refinements are lexical in scope2.
Thus the top level method that defined by the Refinements couldn't breaks other libraries code, It's totally fine!

# Rakefile require_relative 'duck.rb' main = self using Module.new { refine(main.singleton_class) do def puts(*) print 'Hi! ' super end end } desc 'hi' task :hi do duck = Duck.new('Donald') puts duck.name duck.sound end
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$ rake hi Hi! Donald quack
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Other approach

Wrap the method and DSLs within a module.

# Rakefile require_relative 'duck.rb' Module.new { def puts(*) print 'Hi!, ' super end extend(self) extend Rake::DSL desc 'hi' task :hi do duck = Duck.new('Donald') puts duck.name duck.sound end }
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$ rake hi Hi!, Donald quack
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  1. e.g. Rakefile, config/routes.rb, unicorn.rb, etc... ↩

  2. https://docs.ruby-lang.org/en/trunk/syntax/refinements_rdoc.html#label-Scope ↩

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