|||除非包含？各色？

Question

以下两行之间有什么区别？

# settings and globals are Hash 
@settings[:xvfb] = globals[:xvfb] unless settings.include?(:xvfb) 
@settings[:xvfb] ||= globals[:xvfb] 

它们是否相等？

Answer 1

不，它们不是等价的。它们在处理错误的值方面有所不同。

globals = { foo: 'bar' } 

h = { foo: nil } 
h.include?(:foo) # => true 
h[:foo] = globals[:foo] unless h.include?(:foo) 
h # => {:foo=>nil} 

h = { foo: nil } 
h[:foo] ||= globals[:foo] 
h # => {:foo=>"bar"}