Feature #13600: yield_self should be chainable/composable

• Status: Rejected
• Assignee: -
• Target version: -

[avit (Andrew Vit)]

One of the main use cases that would make yield_self a helpful addition is to build functional pipelines (function composition). This is currently not possible since Proc/Lambda do not handle yield_self in the expected way.

I believe that callable.yield_self(&other) should build up a composition, something like this:

class Proc
  def yield_self(&other)
    proc { |input| other.call( self.call(input) ) }
  end
end

I originally proposed an example for this using pipe | syntax here:

https://bugs.ruby-lang.org/issues/10095#note-22

Maybe Proc should use | or & for this syntax instead of changing yield_self directly.

[avit (Andrew Vit)]

In case the description is unclear, the goal is to support something like this:

pipeline = (&:upcase).yield_self(&:reverse)
"ruby".yield_self(pipeline)
#=> "YRUB"

or else:

pipeline = (&:upcase) | (&:reverse)
"ruby".yield_self(pipeline)
#=> "YRUB"

[shyouhei (Shyouhei Urabe)]

• Related to Feature #6284: Add composition for procs added

[shyouhei (Shyouhei Urabe)]

I'm not sure if this should be an extension to yield_self or a separate new method.

[matz (Yukihiro Matsumoto)]

• Status changed from Open to Rejected

Function composition should not be implemented by yield_self.

Matz.