三元运算符串联

Question

Why does

1 == 1 ? 'green' : 1 < 0 ? 'red' : 'yellow'

return red in PHP?

I come from Java and Javascript, where this expression returns green .

Simple fiddle to show it: https://jsfiddle.net/yt0e8t93/

Answer 1

C, C++, Java, and Javascript will evaluate this as

1 == 1 ? 'green' : (1 < 0 ? 'red' : 'yellow')

due to the associativity of the ternary conditional operator being from right to left in all those languages. (This goes way back to before the if statement was even conceived).

But the PHP guys wanted to be different. In PHP, your expression is evaluated as

(1 == 1 ? 'green' : 1 < 0) ? 'red' : 'yellow'

This simplifies to 'green' ? 'red' : 'yellow' 'green' ? 'red' : 'yellow' which in turn is 'red' as 'green' is truthy. If you want it the old-fashioned way then use the parentheses as above.