comparisons-of-references-and-values.md

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Comparisons of References and Values

How are values compared?

PHP

When objects are compared with the comparison operator ==, the objects will be considered equal if their attributes and values match and are both instances of the same class.

When objects are compared with the identity operator ===, the objects will be considered equal if they both refer to the same reference of an object.

<?php
    class myClass {
        public $foo;
        public $bar;
        function __construct($foo, $bar) {
            $this->foo = $foo;
            $this->bar = $bar;
        }
    }

    $a = new myClass("apples", "oranges");
    $b = new myClass("apples", "oranges");
    $c = $a;

    ($a == $b) ? print "a equals b" : print "a does not equal b";
    ($a === $b) ? print "a and b reference the same object" : print "a and b do not reference the same object";
    ($a === $c) ? print "a and c reference the same object" : print "a and c do not reference the same object";
?>

Will yield:

a equals b
a and b do not reference the same object
a and c reference the same object

Python

Equality in Python is compared with the == operator. To check if two objects share the same reference, Python uses the is keyword. However when comparing objects, Python does not necessarily natively verify that the objects are identical purely by value like PHP. This can be resolved by manually overriding the __eq__() method.

class myClass:
    def __init__(self, foo, bar):
        self.foo = foo
        self.bar = bar
    def __eq__(self, other):
        return self.__dict__ == other.__dict__

a = myClass("apples", "oranges")
b = myClass("apples", "oranges")
c = a

print("a equals b") if (a == b) else print("a does not equal b")
print("a and c reference the same object") if (c is a) else print("a and c do not reference the same object")

Will yield:

a equals b
a and c reference the same object