PHP
Closure binding (bindTo)
Learn to bind a closure to a different object with bindTo().
Binding $this with bindTo
A closure cannot use $this in the context where it was defined. But with bindTo($newThis) it binds to a different object; $this now points to that object.
For example $cb = function () { return $this->name; }; cannot be called on its own. $cb->bindTo($obj) returns a new closure where $this is $obj.
This is a powerful way to reuse closures across classes; it acts like a fake method.
The Closure::bind static method
Closure::bind($cb, $newThis, $scope) is a static method. It does the same job as bindTo but does not touch the original closure; it returns a new one.
The third parameter $scope decides from which class visibility scope $this is seen. To access private fields you pass the class name.
Which one to pick is a matter of style: bindTo is object-oriented, Closure::bind is a static call.
Exercise Bind a closure to a stdClass
Define a closure named $greet: function () { return 'Hello ' . $this->name; }. Create an object with $obj = new stdClass; and assign $obj->name = 'Alex';. Bind the closure to $bound with bindTo($obj). Print the result with echo $bound() . "\n";.
Show example solution
Write $greet = function () { return 'Hello ' . $this->name; };. Set $obj = new stdClass; $obj->name = 'Alex';. Bind with $bound = $greet->bindTo($obj);. Write echo $bound() . "\n";.
Example solution:
<?php
// Bind the closure to a stdClass object with bindTo
$greet = function () {
return 'Hello ' . $this->name;
};
$obj = new stdClass;
$obj->name = 'Alex';
$bound = $greet->bindTo($obj);
echo $bound() . "\n";
Test yourself
-
Complete the bindTo call
<?php
$greet = function () { return $this->name; };
$obj = new stdClass;
$obj->name = 'Alex';
$bound = $greet->____($obj);
echo $bound() . "\n";
Show answer
<?php
$greet = function () { return $this->name; };
$obj = new stdClass;
$obj->name = 'Alex';
$bound = $greet->bindTo($obj);
echo $bound() . "\n";
-
Match the binding concepts
- bindTo()
- Instance method
- Closure::bind()
- Static method
- $this
- Bound object
- scope
- Visibility scope
-
What does bindTo do?
- Binds the closure to a new $this
- Deletes the closure
- Turns the closure into an array
- Converts the closure to text
Show answer
Binds the closure to a new $this — Correct. bindTo($obj) binds the closure to a new object; $this becomes $obj.
Next lesson: Summary - Closures and callbacks
