[ruby-core:90978] [Ruby trunk Feature#15477] Proc#arity returns -1 for composed lambda Procs of known arguments

Issue #15477 has been updated by matz (Yukihiro Matsumoto).


Yes, please.

Matz.


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Feature #15477: Proc#arity returns -1 for composed lambda Procs of known arguments
https://bugs.ruby-lang.org/issues/15477#change-76191

* Author: robb (Robb Shecter)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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```
f = -> x { x + 2 }
g = -> x { x * 2 }
h = f << g

f.arity # => 1
g.arity # => 1
h.arity # => -1  THIS SHOULD BE 1 because h "knows" that it takes exactly 1 argument:
h.call  # => ArgumentError (given 0, expected 1)
```

Lambda Procs which are composed using `<<` seem to partially lose knowledge of their arity. I don't know if this affects other procs, or the `>>` operator as well. The Proc#arity docs state that -1 is returned only when a variable or unknown number of arguments are expected by the Proc. But here, that's not the case.



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