corresponding nested ternary operator in php?

问题

I want to convert following if else condition to nested ternary operator.

if ($projectURL) {
    echo $projectURL;
} elseif ($project['project_url']) {
    echo $project['project_url'];
} else {
    echo $project['project_id'];
}

I have written like following.

echo ($projectURL)?$projectURL:($project['project_url'])?$project['project_url']: $project['project_id'];

But it is found as not working properly.Is this not a right way?

回答1:

Ternary operators are tricky thing in PHP, as they are left-associative (unlike all other languages, where it's right-associative). You will need to use parenthesis to tell PHP what you want exactly in this case:

echo ($projectURL ? $projectURL : ($project['project_url'] ? $project['project_url'] : $project['project_id']));

回答2:

As of php 7 we can use Null coalescing operator

echo $projectURL ?? $project['project_url'] ?? $project['project_id'];

来源：https://stackoverflow.com/questions/32244527/in-which-order-are-nested-short-hand-assignments-evaluated