symfony container: injected class's constructor not called

Question

When I inject a service into another via constructor injection, the constructor of the injected class is not being called. Has anyone an explanation for this. What am I overlooking?

I created this little sample for demonstration purposes:

services.yml

services:
    foo.A:
        class: Acme\FooBundle\A

    foo.B:
        class: Acme\FooBundle\B
        arguments:
            a: "@foo.A"

Class A:

<?php

namespace Acme\FooBundle;

class A
{
    public function __construct()
    {
        echo "constructing A\n";
    }
}

Class B:

<?php

namespace Acme\FooBundle;

class B
{
    public function __construct($a)
    {
        echo "constructing B\n";
    }
}

Testcode:

echo "\nTest A ----------------------\n";
$this->getContainer()->get('foo.A');

echo "\nTest B ----------------------\n";
$this->getContainer()->get('foo.B');

Output:

Test A ---------------------- constructing A

Test B ---------------------- constructing B

When retrieving 'foo.B' I'd expect that also A's constructor would be called.

Answer 1

As you've called $this->getContainer()->get('foo.A'); before $this->getContainer()->get('foo.B'); there is already instance of class A so it's not created again.

Try to call only $this->getContainer()->get('foo.B'); and you'll get output of both constructors