赋值运算符和条件运算符的运算符优先级
我正在读一本关于 Ruby 1.8 和 1.9 的书，名为“The Ruby Programming Language”。书中说 if 运算符的优先级低于赋值运算符。如果这是真的，那么我不明白这个表达式是如何工作的：
如果为假，则 x = 5
如果赋值运算符具有更高的优先级，那么它应该在 if 运算符之前执行。因此，在执行 if false 之前，应将 5 赋给 x。
我是否误解了优先顺序？
I'm reading a book called "The Ruby Programming Language" for Ruby 1.8 and 1.9. The book says that if-operator has a lower precedence than an assignment-operator. If this is true then I don't understand how this expressions works:
x = 5 if false
If assignment-operator has a higher precedence then it should be executed before an if-operator. So, 5 should be assigned to x before if false is executed.
Am I misunderstanding precedence?
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较高的赋值优先级意味着表达式的计算结果为
(x = 5) if false，而不是x = (5 if false)。请注意，稍后也是一个完全有效的表达方式。每个特定子句是否被执行是由语言规则决定的。例如，在三元运算符
a ? b : c，仅执行b或c，但不会同时执行两者。编辑
关于差异。
在
x = (5 if false)中，首先处理赋值。但要完成它，我们需要赋值的左侧部分，即 nil，因为5 if false的计算结果为nil。因此，该表达式相当于 x = nil。在
(x = 5) if false中，首先处理条件运算符。根据其规则，我们首先必须评估条件（false）。由于它是false，所以没有什么可做的，评估结果是nil。希望这是清楚的。
Higher precedence of assignment means that your expression evaluates to
(x = 5) if false, and not tox = (5 if false). Note, that later is a perfectly valid expression too.Whether each particular clause is executed is determined by language rules. E.g., in a ternary operator
a ? b : c, onlyborcwill be executed, but not both.edit
About the difference.
In
x = (5 if false), assignment is processed first. But to complete it, we need left part of assignment, which isnil, because5 if falseevaluates tonil. So, the expression is equivalent ofx = nil.In
(x = 5) if false, conditional operator is processed first. According to its rules, we first have to evaluate condition (false). Since it'sfalse, there's nothing more to do and result of evaluation isnil.Hope that's clear.
因为
; if 显然，
假。Because
<expr> if <condition>is not a one expression. It is a special syntaxic sugar of Ruby. It works just like:where, obviously,
<expr>must be evaluated only after<condition>because<condition>can befalse.