为什么表达式(true == true == true)会产生语法错误? [英] Why does the expression (true == true == true) produce a syntax error?

问题描述

Ruby :

 true == true == true
 

语法错误，意外的tEQ

vs. JavaScript :

 true == true == true
// => true
 

vs. C :

 1 == 1 == 1
// => 1
 

与===，==方法定义关联方向，该方向控制操作符对其参数进行求值的运算符的顺序. >，=~和<=>方法(所有方法都具有相同的优先级，并且排他地形成一个单独的优先级组).

文档

因此，在上述列表中有多个运算符排成一行的情况下，评估顺序应通过任一方法明确设置

• 括号():

  (true == true) == true # => true
  true == (true == true) # => true
  

• 或点运算符.(对于连续的最后一次相等检查，可以省略 ):

  true .== true == true # => true
  

Ruby:

true == true == true

syntax error, unexpected tEQ

vs. JavaScript:

true == true == true
// => true

vs. C:

1 == 1 == 1
// => 1

解决方案

Association direction, which controls the order of operators having their arguments evaluated, is not defined for the == method, same as for ===, !=, =~ and <=> methods as well (all of which have the same precedence and form a separate precedence group exclusively).

Documentation

Thus evaluation order in case of multiple operators from the list mentioned above being chained in a row should be set explicitly via either

• parenthesis ():

  (true == true) == true # => true
  true == (true == true) # => true
  

• or dot operator . (can be omitted for the last equality check in a row):

  true .== true == true # => true
  

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