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Bug #15357

Proc#parameters returns incomplete type information

Added by larskanis (Lars Kanis) 9 months ago. Updated 9 months ago.

Status:
Open
Priority:
Normal
Assignee:
-
Target version:
-
ruby -v:
ruby 2.5.3p105 (2018-10-18 revision 65156) [x86_64-linux]
[ruby-core:90135]

Description

The current implementation of Proc#parameters differentiate between lambda? true and false.
This is presumably due to the fact, that procs use tricks to apply arguments differently than lambda and methods.

Unfortunately proc{}.parameters states all :req parameters as :opt, so that these both types of parameters are not distinguishable. This information loss leads to the situation that two different proc signatures return an equal parameters list, but behave differently:

pr = proc{|a,b=2| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [:a, 2]  # :a is interpret as the first parameter

pr = proc{|a=1,b| [a,b] }
pr.parameters  # => [[:opt, :a], [:opt, :b]]
pr.call(:a)    # => [1, :a]  # :a is interpret as the second parameter

That means that the current return values of proc{}.parameters are not suitable to build wrapper or proxy objects for a proc. In Eventbox a workaround is used: The proc is passed to define_method and the method parameters are retrieved instead. That way the list of parameters can be retrieved including :req and :opt differentiation, so that a wrapper proc can be built.

The application of argument assignment tricks is a property of the Proc object - not a property of single parameters. Therefore it shouldn't be applied to Proc#parameters in addition - at least not in a way that discards valuable information. The property of the Proc object is already readable through Proc#lambda?, so that there's no need to apply this property to Proc#parameters as well.

My proposal is to unify proc{}.parameters and lambda{}.parameters, so that proc{}.parameters shows positional arguments without default value as type :req as well.

History

#1

Updated by larskanis (Lars Kanis) 9 months ago

  • Description updated (diff)
  • Subject changed from Unify proc{} and lambda{}.parameters to Proc#parameters returns incomplete type information

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