The document explains the use and purposes of interfaces, abstract classes, and traits in programming, emphasizing how interfaces allow for flexibility in class structure and can help in collaborative coding environments. It also details when to use interfaces and abstract classes based on class instantiation, shared code requirements, and method access. Additionally, it highlights the distinction between interfaces, inherited classes, and traits in terms of design patterns and relationships.

1. When & Why
Interfaces, Abstracts, Traits

2. Interfaces: Primary Purposes
Interfaces allow you to define/create a common structure for your classes – to
set a standard for objects.
Interfaces solves the problem of single inheritance – they allow you to inject
‘qualities’ from multiple sources.
Interfaces provide a flexible base/root structure that you don’t get with
classes.
Interfaces are great when you have multiple coders working on a project – you
can set up a loose structure for programmers to follow and let handle details.

3. Interface: When to use
If you have a class that is never directly instantiated in your program, this is a
good candidate for an interface. In other words, if you are creating a class to
only serve as the parent to other classes, it should probably be made into an
interface.
When you know what methods a class should have but you are not sure
what the details will be.
When you want to quickly map out the basic structures of your classes to
serve as a template for others to follow – keeps the code-base predictable
and consistent.

4. Built-In Interfaces
Traversable
Iterator
IteratorAggregate
Throwable
ArrayAccess
Serializable
Closure
Generator

5. Abstract Class: When to use
You want to share code among several closely related classes.
You expect that classes that extend your abstract class have many
common methods or fields or require access modifiers other than public
(such as protected and private).
You want to declare non-static or non-final fields. This enables you to define
methods that can access and modify the state of the object to which they
belong.

6. Trait
Cannot type hint for trait
Can be used to fulfill and interface
Can include more then one
Consistency, DRY

7. Tip
Interface
Think “able”
May be implemented in different ways
Inheritance
Think “is-a”
Many things work the same way
Trait
Think “has-a”

8. Extra Patterns
Singletons
Factories
Collections
Dependency Injection

9. Alena Holligan
• Wife, and Mother of 3 young children
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• Portland PHP User Group Leader
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@alenaholligan alena@holligan.us https://joind.in/talk/0cf82