Interfaces and helper trait for comparing objects.

Equalable interface

$this->equals($that); // True if $this is equal to $that

Comparable interface

Extends Equalable interface

$this->greaterThan($that);        // True if $this is greater than $that
$this->greaterThanOrEqual($that); // True if $this is greater than or equal to $that
$this->lessThan($that);           // True if $this is less than $that
$this->lessThanOrEqual($that);    // True if $this is less than or equal to $that

//  0 if $this is equal to $that
// -1 if $this is less than $that
//  1 if $this is greater than $that
$this->compare($that);

Comparison trait

A class using this trait only has to implement the compare() method.

Methods equals(), greaterThan(), greaterThanOrEqual(), lessThan() and lessThanOrEqual() will be provided by the trait, based on the result of compare().