问题
This leads to the situation like:
-1 ** 0.5 #=> -1
Only parenthesis remedies it:
(-1) ** 0.5 #=> 6.123031769111886e-17+1.0i
which is less favorable then expected 1.i, but basically acceptable. Before I go to Ruby bugs to complain, I would like to know whether there is perhaps some reason for this to be so?
回答1:
Many languages define their operator precedence tables by modeling after mathematics' order of operations. In math, exponentiation does have higher precedence than multiplication, and unary negation is a multiplication, after all.
From matz in a reply to "the sign of a number is omitted when squaring it":
People with mathematical background demands precedence for ** being higher than that of unary minus. That's the reason.
回答2:
Yes, ** has a higher precedence in Ruby.
Unlike some languages, - is not lex'ed as part of the number literal and is thus just (and universally) the unary - (aka -@). That is, both -x and -1 parse the unary -@ as an operator applied to the result of the expression.
来源：https://stackoverflow.com/questions/13329083/why-does-ruby-operator-have-higher-precedence-than-unary