What's the difference between Singleton and Registry design pattern

Question

I have some confusion between those two patterns:

singleton
Check if the instance exists return it, or create a new one.

Registry
Check if the instance exists return it, or create a new one and store it.

What the difference between them?

Answer 1

Both are about instance control. The difference is that Singleton allows only one instance of a given class while Registry holds a 1-1 map of keys to instances. Typically, the key is (or represents) a class and the value is an instance of that class.

For example, Code Igniter framework holds a registry with an instance of each library/model/controller/helper you load and returning those same instances every time.

Answer 2

A Registry differs in that its principal purpose is to allow you to navigate to associated objects. See Martin Fowler.

Answer 3

The main difference between registry and singleton is that singleton allow us to create a single instance of a class at a time, whereas registry allows us to create multiple instance of the same class.