Can you explain the structure and features of the type system in PHP?

In PHP, the type system is dynamic and weakly typed, which means variables do not require explicit type declaration, and types can be automatically converted when necessary.

Features:

• Dynamic typing: the variable type is determined at runtime.
• Weak typing: PHP attempts to automatically convert types during operations (for example, the string "5" can be used as the number 5).
• Scalar types: int, float, string, bool.
• Complex types: array, object, callable, iterable.
• Return and argument types: starting from PHP 7, you can specify types for function parameters and return values, increasing strictness.
• Nullable types: it is possible to specify that a parameter or return value can be of a certain type or null.

Example of a function declaration with types:

function sum(int $a, int $b): int {
    return $a + $b;
}

If arguments of a different type are passed, PHP will attempt to convert them or throw an error in strict mode.