In symfony, what is a bag?

Question

I've found a decent answer regarding what is a bag in the context of java: What is meant by the term "bag"?

I did a google search and found that Symfony provides a lot of different "bag" interfaces like this one:

http://api.symfony.com/2.3/Symfony/Component/DependencyInjection/ParameterBag/ParameterBag.html

In symfony, is the term bag meant to be interpreted as the same way? Also, how is this different from a "container" or "collection".

Answer 1

A bag (the object's name is ParameterBag) contains variables or parameters.

A collection contains a list of elements (think of it as an oriented-object version of array with a lot of useful methods to manipulate the values). The object comes from the Doctrine framework. Symfony also has a concept of Collection and it is explained in its documentation.

A Container contains all kind of objects, it has its own ParameterBag object with its parameters loaded from anything within the parameters key of your config file.

A Request object ($this->container->get('request')) also has its own ParameterBag.

Code-wise, the Container's parameter bag and the Request's parameter bag are different and could have different methods but their goals are identical.

Answer 2

A bag is short for ParameterBag. A bag is a datatype used to help store data, similar to a collection in java. A bag specifically can access values via key/value as Dagon pointed out, but also has other operations that are useful.

The public operations of a bag are: clear, add, all, get, set, has, remove, resolve, resolveValue, resolveString, isResolved, escapeValue, and unescapedValue.

If you'd like to see the operations of a bag in detail, you can do so here: https://github.com/symfony/symfony/blob/master/src/Symfony/Component/DependencyInjection/ParameterBag/ParameterBag.php