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Feature #16166

closed

Remove exceptional treatment of *foo when it is the sole block parameter

Added by sawa (Tsuyoshi Sawada) about 3 years ago. Updated 7 months ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Target version:
-
[ruby-core:94925]

Description

In the parameter signature of a code block for a method that is not involved in method definition or creation of lambda objects, two types of arguments ["a"] and "a" are neutralized:

instance_exec(["a"]){|foo, bar| foo} # => "a"
instance_exec("a"){|foo, bar| foo} # => "a"

instance_exec(["a"]){|*foo, **bar| foo} # => ["a"]
instance_exec("a"){|*foo, **bar| foo} # => ["a"]

This is the same behavior as with assignment constructions:

foo, bar = ["a"]; foo # => "a"
foo, bar = "a"; foo # => "a"

*foo = ["a"]; foo # => ["a"]
*foo = "a"; foo # => ["a"]

And it contrasts with constructions involved in method definition or creation of lambda objects, where the distinction is preserved:

lambda{|foo| foo}.call(["a"]) # => ["a"]
lambda{|foo| foo}.call("a") # => "a"

->(foo){foo}.call(["a"]) # => ["a"]
->(foo){foo}.call("a") # => "a"

lambda{|*foo| foo}.call(["a"]) # => [["a"]]
lambda{|*foo| foo}.call("a") # => ["a"]

->(*foo){foo}.call(["a"]) # => [["a"]]
->(*foo){foo}.call("a") # => ["a"]

However, when *foo is the sole parameter of a code block for a method that is not involved in method definition or creation of lambda objects, ["a"] and "a" are not neutralized:

instance_exec(["a"]){|*foo| foo} # => [["a"]]
instance_exec("a"){|*foo| foo} # => ["a"]

behaving in contrast to assignment constructions, and rather on a par with constructions involved in method definition or creation of lambda objects.

Particularly, existence or absence of another parameter **bar entirely changes what foo refers to:

instance_exec(["a"]){|*foo| foo} # => [["a"]]
instance_exec(["a"]){|*foo, **bar| foo} # => ["a"]

I find this behavior inconsistent and confusing. I would like to request to remove this exceptional treatment of splatted parameter *foo when it is the sole parameter in a code block. I request this behavior:

instance_exec(["a"]){|*foo| foo} # => ["a"]
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