Ruby 2.1.0, 2.0, 1.9, 1.8

operator是表示要对一个或多个操作数执行的操作(如加法或比较)的标记.操作数是表达式，运算符允许我们将这些操作数表达式组合成更大的表达式.(Ref)

N=arity=运算符操作的操作数.(Ref)

A=associativity=同一运算符(或具有相同优先级的运算符)在表达式中顺序出现时的求值顺序.值L表示表达式从left to right计算.值R表示表达式从right to left计算.值N表示运算符为nonassociative，不能在没有括号的表达式中多次使用，以指定计算顺序.(Ref)

M=definability=Ruby实现了许多操作符作为方法，允许类为这些操作符定义新的含义.的第M列指定哪些运算符是方法.标记为Y的运算符用方法实现，可以重新定义，标记为N的运算符不能.(Ref)

下表按降序排列(highest precedence at the top).

N A M  Operator(s)            Description
- - -  -----------            -----------
1 R Y  ! ~ +                  boolean NOT, bitwise complement, unary plus
                              (unary plus may be redefined from Ruby 1.9 with +@)

2 R Y  **                     exponentiation
1 R Y  -                      unary minus (redefine with -@)

2 L Y  * / %                  multiplication, division, modulo (remainder)
2 L Y  + -                    addition (or concatenation), subtraction

2 L Y  << >>                  bitwise shift-left (or append), bitwise shift-right
2 L Y  &                      bitwise AND

2 L Y  | ^                    bitwise OR, bitwise XOR (exclusive OR)
2 L Y  < <= >= >              ordering

2 N Y  == === != =~ !~ <=>    equality, pattern matching, comparison
                              (!= and !~ may not be redefined prior to Ruby 1.9)

2 L N  &&                     boolean AND
2 L N  ||                     boolean OR

2 N N  .. ...                 range creation (inclusive and exclusive)
                              and boolean flip-flops

3 R N  ? :                    ternary if-then-else (conditional)
2 L N  rescue                 exception-handling modifier

2 R N  =                      assignment
2 R N  **= *= /= %= += -=     assignment
2 R N  <<= >>=                assignment
2 R N  &&= &= ||= |= ^=       assignment

1 N N  defined?               test variable definition and type
1 R N  not                    boolean NOT (low precedence)
2 L N  and or                 boolean AND, boolean OR (low precedence)
2 N N  if unless while until  conditional and loop modifiers