PHP将类传递给另一个类并使用其中的常量

Question

I'm trying to use a constant from a class that I'm passing to another class, but I can't work out how to call it. Can anyone point out where I'm going wrong:

Class A {
    const TEST = 1;

}

Class B {
    protected $c;

    function func($c) {
        $this->c = $c;

        echo $this->c::TEST; // this doesn't work
    }
}

$a = new A();
$b = new B();

$b->func($a);

Answer 1

Accessing constants on instances on properties is only a syntactical ambiguity/incompatibility in PHP versions < 7. What you're doing work fine in versions >= 7. This works just fine in all versions:

function func($c) {
    echo $c::TEST;
}

In PHP < 7, you'll have to resort to:

$c = $this->c;
$c::TEST;

Answer 2

Since TEST is a constant, you access it statically, like A::TEST

Check the PHP manual: http://php.net/manual/en/language.oop5.constants.php

Answer 3

This only works in php 7.

What you can do in PHP 5 is replace your:

echo $this->c::TEST; 

with:

echo A::TEST;

or:

echo $c::TEST;

Answer 4

Class A {
  const TEST = 1;
  function getText()
  {
   return static::TEST;
  }
}

then use this function (notice static keywords for Inheritance)

Class B {
    protected $c;

    function func($c) {
        $this->c = $c;

        echo $this->c->getTest();
    }
}