ruby - 如何调用 ruby​​ 块来访问调用者绑定

Question

我想访问调用者的绑定。这里有什么问题？

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

为什么我无权访问给定块内的调用者实例？

Answer 1

在块内部，您不在Blocks实例范围内，因此foo不可见。如果你想访问它，你必须将对象传递给块：

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

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

或者，您可以将块传递给instance_eval：

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

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

Answer 2

试图重现它：

3.times.map{ foo }
#~>  undefined local variable or method `foo' for main:Object (NameError)

内部{ }或外部{}，foo尚未定义为 amethod或varable。因此 Ruby 解析器感到困惑并抛出错误。

现在看：

foo = 12
3.times.map{ foo }
# => [12, 12, 12]

尝试 ：

test "say method_foo" do
  assert_equal( 'foo', Blocks.new{|i| i.foo }.run )
end

Answer 3

尝试这个

class Blocks
  def initialize( &block ); @block = block; end
  def run; instance_eval &@block; end

  def foo; 'foo'; end
end