Which Values Are Considered Falsy in PHP?

Falsy values are values that are considered equivalent to false in PHP when evaluated in a boolean context. According to the official PHP docs, the following values are considered to be falsy:

1. Boolean false;
2. Integer 0;
3. Float 0.0 and -0.0;
4. Empty String;
5. String "0";
6. Array with no elements, [];
7. NULL type;
8. Some internal objects, like SimpleXML objects created from empty elements (i.e. elements that have no children and attributes), may behave as falsy when explicitly converted to boolean.

These values evaluate to a boolean false when:

1. They're explicitly converted to a boolean (for example by casting);
2. An operator, function or control structure requires a boolean argument (in which case the value is converted to a boolean implicitly/automatically).

For example:

echo var_dump((bool) false); // false
echo var_dump((bool) 0); // false
echo var_dump((bool) 0.0); // false
echo var_dump((bool) ''); // false
echo var_dump((bool) '0'); // false
echo var_dump((bool) []); // false
echo var_dump((bool) null); // false
echo var_dump((bool) new SimpleXMLElement('<foo />')); // false