Feature #6869

Updated by nobu (Nobuyoshi Nakada) about 5 years ago

I started by commenting on #6693, but i have realized that this is a slightly different request.

I propose to not treat the variable name "`_`" "(({_}))" exceptionally. Current behavior:


{0=>1}.each_with_index { |_,_| p _ } # [0, 1]

prints "[0, 1]", but


{1=>2}.each_with_index { |x,x| p x } # SyntaxError: (eval):2: duplicated argument name

raises "SyntaxError: (eval):2: duplicated argument name".

Similarly for methods:


def f(_, _)
f(0, 1) # => 0

def f(x, x)
end # => SyntaxError: (eval):2: duplicated argument name

Observe also that the use of repeated `_` (({_})) parameter is not consistent between methods and blocks: for methods the value is the first assigned value, and for blocks it is the array of all the assigned values.

1. I propose to use the same rule for all variables, without distinguishing `_` (({_})) specially.

In particular i propose to allow to repeat any variable, not only `_`, (({_})), in block or method arguments without raising an error.

There may be several solutions what the repeated argument will hold: it may hold the array of all assigned values, the first assigned value, the last assigned value, the first non-nil assigned value, or the last non-nil assigned value.

2. I propose to treat repeated arguments in methods and in blocks the same way (do not know which one).

3. For unused variables i propose to introduce a special placeholder, for example "`-`" "(({-}))" not followed by anything other than a delimiter (comma or bracket):


each_with_index { |-, value| puts value }

-, -, suffix = parse(name)