No Cast In Constant Expressions

<?php

class x {
    const string A = '42';
    const int B = +self::A;
    // This, below, is a compile error
    const int C = (int) self::A;

}

Constant expressions do not accept the cast operator.

Constant expressions are expressions defining constants and default values. They allow a subset of PHP features, as they are available before the execution phase. For example, they accept operators, such as addition and concatenation. Yet, they do not accept the cast operators, even though they might be emulated in another way. Here, the + operator creates the integer, from another string.

See Also

• Class constants (PHP manual)

• const cannot cast [Try me]

PHP Error Messages

• Constant expression contains invalid operations

PHP Features

• cast

• constant-expression

Last updated: 14 July 2026