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Setting constant values

From: Object-Oriented Programming with PHP

Video: Setting constant values

There's a strong possibility that you're already familiar with constants. They are common place in procedural code. As a natural extension, it's possible to add a constant to a class, which can be good for code organization. A class constant is like a property with a value that never changes. Constants are useful for defining things like error codes, data structure names, and values that have no need to change at runtime, if ever. By associating a constant with a class, a developer can add context rather than having to resort to long, complicated names.

Setting constant values

There's a strong possibility that you're already familiar with constants. They are common place in procedural code. As a natural extension, it's possible to add a constant to a class, which can be good for code organization. A class constant is like a property with a value that never changes. Constants are useful for defining things like error codes, data structure names, and values that have no need to change at runtime, if ever. By associating a constant with a class, a developer can add context rather than having to resort to long, complicated names.

While constants use the same PHP label naming convention, best practice dictates that constant names are all in capital letters separated by underscores. Constants can only contain simple values, so strings, booleans and integers will work, but an array will not. To define a constant within a class, start with the keyword "const," followed by the name with no dollar sign ($), an assignment operator, and a value. Let's said add constant to the address class to store the address type IDs.

I'm going to open the Address class, and navigate to the top of the file, then add three constants for each of the address type values. const ADDRESS_TYPE_RESIDENCE = 1, const ADDRESS_TYPE_BUSSINESS = 2, and then const ADDRESS_TYPE_PARK = 3. Part of the reason why I did not specify that the address types be defined as a constant is that arrays are not allowed as constant values. With that said, you can replace the hardcoded values with the constants that were just declared.

Similar to static properties, you use the scope resolution operator to access constants, only without the dollar sign ($). Edit the static address types, and replace the keys with the constant values. Address::ADDRESS_TYPE_RESIDENCE, Address::ADDRESS_TYPE_BUSSINESS and Address::ADDRESS_TYPE_PARK and save. There is no functional difference between having the raw numbers there in the constants, which is part of the goal.

The advantage is that there's only one place where those values are set, which makes them available to any other code. I can refer it to these address type IDs with semantic human readable names, as opposed to trying to have to remember what number is associated with them. In a moment, I'll demonstrate how to write a static method for validating address type IDs using these class constants. From a code maintainability perspective, those constant values are now available to any other piece of code, and can be referenced using semantic names, as opposed to trying to remember what number is associated with which value.

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Object-Oriented Programming with PHP

37 video lessons · 17662 viewers

Jon Peck
Author

 
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  1. 4m 10s
    1. Welcome
      39s
    2. Exercise files
      2m 16s
    3. What you should know
      1m 15s
  2. 7m 47s
    1. What is an object?
      2m 6s
    2. What is a class?
      2m 7s
    3. Why should you use object-oriented programming?
      2m 14s
    4. The history of object-oriented PHP
      1m 20s
  3. 16m 40s
    1. Defining a class
      2m 58s
    2. Defining class properties
      3m 26s
    3. Creating a method and exploring object context with $this
      2m 50s
    4. Instantiating an object and accessing its contents
      3m 19s
    5. Specifying the visibility scope
      4m 7s
  4. 15m 51s
    1. What is a magic method, and do I need one?
      2m 23s
    2. Overloading property access
      6m 37s
    3. Customizing object construction
      4m 34s
    4. Standardizing object rendering as a string
      2m 17s
  5. 20m 54s
    1. Using the static keyword
      3m 36s
    2. Leveraging scope resolution operators
      1m 10s
    3. Setting constant values
      2m 47s
    4. Implementing static methods
      5m 43s
    5. Creating a database class
      7m 38s
  6. 26m 19s
    1. Extending your class
      6m 8s
    2. Abstracting classes
      5m 57s
    3. Sharing interfaces using polymorphism
      4m 39s
    4. Overriding methods, properties, and constants
      3m 25s
    5. Cloning and comparing objects
      2m 51s
    6. Referencing objects
      3m 19s
  7. 14m 52s
    1. Leveraging standard class objects
      2m 42s
    2. Retrieving objects from the database
      5m 41s
    3. Error handling with exceptions
      2m 6s
    4. Customizing PHP exceptions
      4m 23s
  8. 8m 2s
    1. Identifying the singleton pattern
      1m 42s
    2. Using the factory method pattern
      1m 51s
    3. Implementing a strategy pattern
      4m 29s
  9. 2m 57s
    1. Looking forward to namespaces
      47s
    2. Next steps
      1m 6s
    3. Goodbye
      1m 4s

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