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Feature #16166

Updated by sawa (Tsuyoshi Sawada) 10 months ago

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: 

 ```ruby 
 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: 

 ```ruby 
 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: 

 ```ruby 
 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: 

 ```ruby 
 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: 

 ```ruby 
 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 handling of a splatted parameter `*foo` when it is the sole parameter in a code block. I request this behavior: 

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

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