php - PHP 解析错误：语法错误，意外的 ':'

Question

很长一段时间我都用过这样的东西：

$foo = $foo ?: $bar; // similar to $foo = $foo ? $foo : $bar;

它运作良好。

但现在我在使用PHPVersion of的新主机上5.2.17，当我尝试运行类似的代码时，它显示一个解析错误：

Parse error: syntax error, unexpected ':' in /../

我该如何解决这个问题？

Answer 1

缩短的三元语法仅在PHP 5.3 和更新版本中可用

Answer 2

Please note that the ternary operator is a statement, and that it
doesn't evaluate to a variable, but to the result of a statement. This
is important to know if you want to return a variable by reference.
The statement return $var == 42 ? $a : $b; in a return-by-reference
function will therefore not work and a warning is issued in later PHP
versions.

So there is a problem with the return-by-reference for the ?: syntax.
That's way I explicitly wrote what should be returned. 

参考站点https://groups.google.com/forum/#!msg/doctrine-user/qbSAvaKH5uI/DF_2XSxFvG4J

我不能说它有一个bug，但从网址https://bugs.php.net/bug.php?id=60169看来bug

there is also segfault in (***)?:value notation.
like:
   <?php
     $str = array('test');
     list($a, $b) = is_array($str)?:$str;

and this make *the patch doesn't work* (a memory leak)