Question

我有两个例子：

第一

CircleMenuDelegate.circleMenu(**Circle Menu Object Here**, buttonWillSelected: UIButton, atIndex: Int)

结果：

class SomeClass
  attr_accessor :some_var
  def initialize
    @some_var = 42
    yield self if block_given?
  end
end

p some_instance = SomeClass.new
another_instance = SomeClass.new do |s|
  s.some_var = "foobar"
end

p another_instance

第二

#<SomeClass:0x007fcdda047270 @some_var=42>
#<SomeClass:0x007fcdda047130 @some_var="foobar">
[Finished in 0.1s]

结果：

class SomeClass
  attr_accessor :some_var
  def initialize
    @some_var = 42
    yield self if block_given?
  end
end

p some_instance = SomeClass.new
p another_instance = SomeClass.new do |s|
  s.some_var = "foobar"
end

p another_instance

我期待得到：

#<SomeClass:0x007fdd3f0131e0 @some_var=42>
#<SomeClass:0x007fdd3f0130a0 @some_var=42>
#<SomeClass:0x007fdd3f0130a0 @some_var=42>
[Finished in 0.1s]

我知道赋值比#<SomeClass:0x007fdd3f0131e0 @some_var=42> #<SomeClass:0x007fcdda047130 @some_var=42> #<SomeClass:0x007fcdda047130 @some_var="foobar"> [Finished in 0.1s]块更贪婪。并且这些curlies比赋值更贪婪，如下所示：

第三

do...end

结果：

p yet_another_instance = SomeClass.new { |s| s.some_var = "foobar" }
p yet_another_instance

但是第二个例子中#<SomeClass:0x007f9a420529c0 @some_var="foobar"> #<SomeClass:0x007f9a420529c0 @some_var="foobar">块会发生什么？它不会被运行吗？

编辑：

接受@ max_pleaner的建议:)似乎Ruby完全忽略了它：

do...end

结果：

class SomeClass
  attr_accessor :some_var
  def initialize
    @some_var = 42
    yield self if block_given?
  end
end

p some_instance = SomeClass.new
p another_instance = SomeClass.new do |s|
  puts "cats and dogs?"
  s.some_var = "foobar"
end

p another_instance

所以现在我很好奇，在什么条件下Ruby完全忽略了一个块？有没有关于这种情况的文件？

编辑：

参见接受的答案

#<SomeClass:0x007fd01f96f130 @some_var=42>
#<SomeClass:0x007fd01f96eff0 @some_var=42>
#<SomeClass:0x007fd01f96eff0 @some_var=42>
[Finished in 0.1s]

结果：

class SomeClass
  attr_accessor :some_var
  def initialize
    @some_var = 42
    yield self if block_given?
  end
end

p some_instance = SomeClass.new
p (another_instance = SomeClass.new do |s|
  puts "cats and dogs?"
  s.some_var = "foobar"
end)

p another_instance

Answer 1

由于{ ... }和begin ... end的优先级不同而产生混淆，并且您不使用括号使其明确。表达式

p another_instance = SomeClass.new do |s|
  puts "cats and dogs?"
  s.some_var = "foobar"
end

被解释为

p(another_instance = SomeClass.new) do |s|
  puts "cats and dogs?"
  s.some_var = "foobar"
end

所以阻止传递给#p，而不是SomeClass#new。您可以明确强制执行其他订单：

p(another_instance = SomeClass.new do |s|
  puts "cats and dogs?"
  s.some_var = "foobar"
end)

并且将以您期望的方式执行该块。

传递给新方法时do..end块会发生什么？

1 个答案: