PHP syntax surprise with conditional operator "?:" and "OR"

Question

Today, I was open-mouthed by the following:

$asdf = ((1 OR true) ? "asdf" : "fdsa");
var_dump($asdf); // print "asdf"

$asdf = (1 OR true) ? "asdf" : "fdsa";
var_dump($asdf); // print "asdf"

$asdf = (1 OR true ? "asdf" : "fdsa");
var_dump($asdf); // print true

$asdf = 1 OR true ? "asdf" : "fdsa";
var_dump($asdf); // print 1

Ok, the last does not surprise me much, but the third? Can anyone explain?

Answer 1

This is all about operator precedence and their associativity

http://php.net/manual/en/language.operators.precedence.php

or has lower precendence than = that is why it will be executed first

so $asdf = 1 OR true ? "asdf" : "fdsa";

will be someting like

($asdf = 1) or true ? :"asdf" : "fdsa" that is why it will print 1.

$a or $b check whether $a or $b is true if $a is true then it is returned and it does not even go to check $b

In third case

$asdf = (1 OR true ? "asdf" : "fdsa");

() has higher precedence than = so it will be executed before assignment.

To prove it

change OR to || which has higher precendence than =

$asdf = 1 || true ? "asdf" : "fdsa";

var_dump($asdf); // print asdf