class Rubocop::Cop::Style::VariableInterpolation

This cop checks for variable interpolation (like “#@ivar”).

def on_dstr(node) 

def on_dstr(node)
  var_nodes(node.children).each do |v|
    var = (v.type == :nth_ref ? '$' : '') + v.to_a[0].to_s
    if node.loc.expression.source.include?("##{var}")
      add_offence(:convention,
                  v.loc.expression,
                  sprintf(MSG, var, var))
    end
  end
  super
end

def var_nodes(nodes) 

def var_nodes(nodes)
  nodes.select { |n| [:ivar, :cvar, :gvar, :nth_ref].include?(n.type) }
end