Issue
I am wondering how Laravel differentiates between singletons(shared instances) and concrete implementations that might be overwritten inside the container.
The container has a bind method that looks like this:
public function bind($abstract, $concrete = null, $shared = false)
{
// If no concrete type was given, we will simply set the concrete type to the
// abstract type. After that, the concrete type to be registered as shared
// without being forced to state their classes in both of the parameters.
$this->dropStaleInstances($abstract);
if (is_null($concrete)) {
$concrete = $abstract;
}
// If the factory is not a Closure, it means it is just a class name which is
// bound into this container to the abstract type and we will just wrap it
// up inside its own Closure to give us more convenience when extending.
if (!$concrete instanceof Closure) {
$concrete = $this->getClosure($abstract, $concrete);
}
$this->bindings[$abstract] = compact('concrete', 'shared');
// If the abstract type was already resolved in this container we'll fire the
// rebound listener so that any objects which have already gotten resolved
// can have their copy of the object updated via the listener callbacks.
if ($this->resolved($abstract)) {
$this->rebound($abstract);
}
}
It also has a singleton method that calls this function but with the $shared argument always being true like so:
public function singleton($abstract, $concrete = null)
{
$this->bind($abstract, $concrete, true);
}
The difference here being that although they both are bound in the $bindings
property the singleton set it like so:
[concrete, true]
How does this make it a singleton though if there seems to be no check if it has already been set or not? Nowhere can I find whether it does anything with the $shared variable we set.
Besides that there is also another property in this class called:
/**
* The container's shared instances.
*
* @var array
*/
protected $instances = [];
It would seem logical for a singleton to end up here, so what exactly does this
Example of the bind method:
https://github.com/laravel/framework/blob/5.3/src/Illuminate/Container/Container.php#L178
Solution
bind()
method saves $shared
here. Then make()
method is using isShared()
method for checking if $shared
is set and then for checking if it's true
or false
here.
Answered By - Alexey Mezenin
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