PHP为foreach（）提供的参数无效

Question

I have this array:

    $y_exceptions = array(
    "lay",
    "interlay",
    "display",
    "delay",
    "obey",
    "decay",
    "play",
    "slay"
);

I'm checking if a word is in my array like this:

foreach($y_exceptions as $thisException) {

Which throws the error

Invalid argument supplied for foreach()

What have I done wrong?

Answer 1

$y_exceptions needs to be an array for it to be processed by a foreach loop. It is possible that $y_exceptions was set to null before the foreach loop. A null is not treated as an array, which the foreach expects—hence the warning.

On solution would be stricter validation before the foreach:

if (!is_array($y_exceptions)) {
    // throw an exception
}

Alternatively, you could instruct the foreach loop to run $y_exceptions as an array, though this may cause errors downstream:

foreach ((array) $y_exceptions as $thisException) {
    // do stuff
}