Symbol#to_proc_with_hash_support

named_block.rb

def key(k)
  ->(obj) { obj[k] }
end

[{ this: 'that' }].map &key(:this)

symbol.rb

class Symbol
  def to_proc
    proc(&method(:to_proc_with_hash_support))
  end

  def to_proc_with_hash_support(obj)
    case obj
    when Hash then obj[self] else send(self)
    end
  end
end

[{ this: 'that' }].map &:this