ruby - 如何调用 ruby​​ block 以访问调用方绑定(bind)

Question

我想访问调用者的绑定(bind)。这里有什么问题吗？

require 'test/unit'

class BlocksTest < Test::Unit::TestCase

  class Blocks
    def initialize( &block ); @block = block; end
    def run; instance_eval { @block.call }; end

    def foo; 'foo'; end
  end

  def test_say_foo_via_string
    assert_equal( 'foo', Blocks.new{ 'foo' }.run )
  end
  # => successful

  def test_say_foo_via_caller_method
    assert_equal( 'foo', Blocks.new{ foo }.run )
  end
  # => NameError: undefined local variable or method `foo'

end

为什么我无法访问给定 block 中的调用方实例？

Answer 1

在 block 内，您不在 Blocks 实例的范围内，因此 foo 不可见。如果你想访问它，你必须将对象传递给 block :

class Blocks
  # ...
  def run
    @block.call(self)
  end
  # ...
end

blk = Blocks.new { |b| b.foo }
blk.run
# => "foo"

或者，您可以将 block 传递给 instance_eval:

class Blocks
  # ...
  def run
    instance_eval(&@block)
  end
  # ...
end

blk = Blocks.new { foo }
blk.run
# => "foo"