php类常量可见性

Question

Can we set visibility of class constant?
For this example:

class MyClass {
    const CONST_VALUE = 'A constant value';
}

Can we specify

public const CONST_VALUE = 'A constant value';

or

private const CONST_VALUE = 'A constant value';

or

protected const CONST_VALUE = 'A constant value';

Answer 1

Update: visibility modifiers for constants have been added in PHP 7.1 (released 1st of December 2016). See the RFC : Support Class Constant Visibility .

The syntax looks like this:

class ClassName {
    private const PRIVATE_CONST = 0;
    protected const PROTECTED_CONST = 0;
    public const PUBLIC_CONST = 0;
}

Answer 2

As of PHP7.1 visibility modifiers are allowed for class constants, in previous versions it's not possible to set the visibility of constants in a class. They're always public. See the comments at http://www.php.net/manual/en/language.oop5.constants.php for more information.

Answer 3

An alternative would be to use a Constant Method, eg

private static function gravitationalConstant() {
    return 9.81;
}

Quoting from Fowler's Refactoring book :

This idiom is less familiar to C based programmers, but is very familiar to Smalltalkers (who didn't have constants in their language). On the whole I don't tend to use this in Java as it is less idiomatic to the language. However if you need to replace the simple return with a calculated value then it's worth changing the constant field to a constant method. (I guess there should be a refactoring for that....)

Answer 4

In PHP Latest version (PHP 7.1.0) it will available.

Sample Syntax was like.

class Token {
    // Constants default to public
    const PUBLIC_CONST = 0;

        // Constants then also can have a defined visibility
        private const PRIVATE_CONST = 0;
        protected const PROTECTED_CONST = 0;
        public const PUBLIC_CONST_TWO = 0;

        //Constants can only have one visibility declaration list
        private const FOO = 1, BAR = 2;
}

Refer below link. https://wiki.php.net/rfc/class_const_visibility

Answer 5

现在可以在PHP 7.1发布Alpha今天添加Class常量可见性修饰符

Answer 6

It is possible in Php 7.1.0. Please visit PHP RFC: Support Class Constant Visibility

Answer 7

Modifiers are not allowed for constants in php. You can use

public static $variable = "abc";

but sadly final is not allowed here.