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Feature #16102

Updated by sawa (Tsuyoshi Sawada) over 2 years ago

Since symbols have a `to_proc` method, it is natural to expect that they would appear in a method chain like: 

 ```ruby 
 :some_symbol.to_proc.call(...) 
 ``` 

 In fact, I have use cases like this: 

 ```ruby 
 arrays = [["a", "b"], ["c"], ["d", "e"]] 
 hashes = [{"a" => 1}, {"b" => 2, "c" => 3}, {"d" => 4, "e" => 5}] 

 :product.to_proc.(*arrays) # => [["a", "c", "d"], ["a", "c", "e"], ["b", "c", "d"], ["b", "c", "e"]] 
 :zip.to_proc.(*arrays) # => [["a", "c", "d"], ["b", nil, "e"]] 
 :union.to_proc.(*arrays) # => ["a", "b", "c", "d", "e"] 
 :merge.to_proc.(*hashes) # => {"a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5} 
 ``` 

 I request `Symbol#call` to be defined, which would implicitly call `to_proc` on the receiver and then the conventional `Proc#call` on the result. Then, I can do: 

 ```ruby 
 :product.(*arrays) # => [["a", "c", "d"], ["a", "c", "e"], ["b", "c", "d"], ["b", "c", "e"]] 
 :zip.(*arrays) # => [["a", "c", "d"], ["b", nil, "e"]] 
 :union.(*arrays) # => ["a", "b", "c", "d", "e"] 
 :merge.(*hashes) # => {"a"=>1, "b"=>2, "c"=>3, "d"=>4, "e"=>5} 
 ``` 

 This would solve what proposals #6499, #7444, #8970, #11262 aim to do. 

 Notice that proposals #12115 and #15301 ask for `Symbol#call`, but they ask for different things (a method that returns a proc), and are irrelevant to the current proposal.

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