Feature #16166
Updated by sawa (Tsuyoshi Sawada) about 5 years 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 treatment 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"]
```