使わないブロックパラメータには'_'をつける。Rubyの構文、良い、悪い例。

_block_parameter.rb

# bad
result = hash.map { |k, v| v + 1 }

def something(x)
  unused_var, used_var = something_else(x)
  # ...
end

# good
result = hash.map { |_k, v| v + 1 }

def something(x)
  _unused_var, used_var = something_else(x)
  # ...
end

# good
result = hash.map { |_, v| v + 1 }

def something(x)
  _, used_var = something_else(x)
  # ...
end

Prefix with _ unused block parameters and local variables. It's also acceptable to use just _ (although it's a bit less descriptive). This convention is recognized by the Ruby interpreter and tools like RuboCop and will suppress their unused variable warnings.