Awesome

WP Lib Loader

jtsternberg.github.io/wp-lib-loader

Utility template class for smartly loading WordPress code libraries.

This is a handy template class for generating smart loaders for your WordPress code libraries and eliminates conflicts and the need for function_exists or class_exists checks in your plugins/themes when including the bundled library. This loader was inspired by CMB2, and is a proven system. It allows any plugin or theme to bundle your library, and only one instance (the most up-to-date version) will be loaded by the system.

It accomplishes this through a semi-magical use of the WordPress hooks system combined with unique loader class-names for each version of the library.

See the background post: Don’t Repeat Yourself. Use WP Lib Loader instead!

Use the generator tool to quickly create a loader for your library!

Getting Started
- Example File
How to version your library
- Example File (version 0.1.1)
Additional details
Super important caveats
Examples in the wild

Getting Started

To use this template, you will need to <del>copy the contents of the loader.php file to your library and then complete a five-step find and replace on the file</del> head over to the generator tool!. As an example, if your library is named WP_Magic:

Search for LIBCLASSNAME and replace with your library's class-name: WP_Magic.
Search for LIBNAMEUPPER and replace with your library's class-name, upppercased (for constants): WP_MAGIC.
Search for LIBNAMELOWER and replace with your library's class-name, lowercased (for hook names): wp_magic.
Search for LIBURL and replace with your library's URL: https://wp_magic.io.
Search for AUTHORNAME and replace with your name: John Doe.
Search for AUTHOREMAIL and replace with your email: john@johndoe.com.

The resulting file:

examples/wp-magic.php

How to version your library

Since the real magic of this loader is when you release a new version, let's walk through that process. Let's say you're looking to release a bug-fix for WP_Magic.

Increase your version numbers to 0.1.1.
- Replace the 0.1.0 for the @version docblocks.
```
* @version  0.1.1
```
- Replace the 0.1.0 for the VERSION constant.
```
const VERSION = '0.1.1';
```
Update the loader class-name from WP_Magic_010 to WP_Magic_011.
MOST IMPORTANT: Decrement the PRIORITY constant.
```
const PRIORITY = 9998;
```

That's it! That's all there is to releasing a new version! You can now be sure that this will be the version used if multiple copies of the library exist.

The resulting file after bumping the version:

examples/wp-magic-version-011.php

Additional details

The loader assumes your main library class (e.g. WP_Magic) exists in the lib/init.php file. Obviously, if that is not the case with your library, you will need to update the require_once line.
Along those lines, this class can be modified/added to if desired, but the core functionality needs to remain.
The loader provides 3 useful constants:
- LIBNAMEUPPER_LOADED (e.g. WP_MAGIC_LOADED) - A constant set right away which dependent plugins/themes can use to determine if your library is loaded (vs function_exists or class_exists checks). This constant can also be used to determine the priority of the hook in use for the currently loaded version.
- LIBNAMEUPPER_VERSION (e.g. WP_MAGIC_VERSION) - Defines the loaded version of your library so dependent plugins/themes have a way to conditionally load features, if needed.
- LIBNAMEUPPER_DIR (e.g. WP_MAGIC_DIR) - Defines the directory of the loaded version of your library. Can be useful for determining the location of the library when debugging and multiple copies of the library exist in the system.
The loader provides a useful hook, 'LIBNAMELOWER_load' (e.g. 'wp_magic_load'), which can be used for hooking in your dependent functionality. To ensure your hook loads after the library is loaded, you will need to use the LIBNAMEUPPER_LOADED (e.g. WP_MAGIC_LOADED) constant when hooking in:
```
if ( defined( 'WP_MAGIC_LOADED' ) ) {

  // Need to hook AFTER the lib.
  $priority = ( WP_MAGIC_LOADED + 1 );
  
  // And add the functionality.
  add_action( 'wp_magic_load', 'my_magic', $priority );
}
```
Keep in mind, the loader includes the library on the first WordPress hook available to it, 'muplugins_loaded', 'plugins_loaded', or 'after_setup_theme'.

Super important caveats

This loader only works if you are 100% committed to backwards-compatibility (like WordPress). This is mandatory because only one instance of the library will be loaded, and will be whichever instance is the most recent (version). If you change a function, hook name, or properties passed into your library hooks, there is a very real chance you will break the plugins/themes which depend on your library. For this reason, you need to take great consideration when developing your public API, i.e. the parts of the library to be exposed for public use.
When releasing a new version, it's extremely important to follow the versioning instructions or this loader will be useless.