Merge pull request #13 from wptrainingteam/plugin-developer-learning-…

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Plugin developer learning pathway/05 good practices

plugin-developer-learning-pathway/02-Advanced-Hooks/04-good-practices.md

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+
+# Good practices
+
+While WordPress hooks are quite easy to begin with, it is however harder to master them.
+
+
+## Naming hooks
+
+The first point comes with naming hooks.
+
+### Actions
+
+As an action involves a change of state, I would advise you to use a verb within its name.
+
+```php
+do_action('delete_post');
+```
+
+Then if the action is happening before the actual event the convention is to prefix it with `pre_`.
+
+```php
+do_action('pre_delete_post');
+```
+
+Finally, if the action is after the actual event, it is advised to use a past tense inside the name.
+
+```php
+do_action('deleted_post');
+```
+
+### Filters
+
+On the other side, a filter is a value and due to that it is advised to use nouns within its name.
+
+```php
+apply_filters('sitemap_url', 'https://example.org/sitemap.xml');
+```
+
+## Handling the filter type mess
+
+When using a filter, the type from the value is never guaranteed even it is set in the docblock.
+
+### The problem
+There is a simple reason for that: It is the last callback that decides what is returned by the filter, and that also means the last callback decides the type from the value.
+
+That might not seem an issue at first, but you need to remember when you are creating your custom hooks that you are not the one who will be writing the callbacks but your users.
+
+![Illustration from the problem](./imgs/handling-filter-return.png)
+
+This means that you have no control on what your users will return and if a wrong type is returned, it might make your plugin crash.
+
+### The solution
+
+The solution for this comes in two parts:
+
+#### Validating your filter output
+
+The best way to make sure the output value is the type we expect is to validate it.
+
+For primitive types as integer, float or boolean, we can cast the output value as following:
+- `boolean`: `$value = (bool) apply_filters('my_filter', true);`
+- `integer`: `$value = (int) apply_filters('my_filter', 10);`
+- `float`: `$value = (float) apply_filters('my_filter', 10.0);`
+
+However, for more complex validation or other types, it is better to have a manual validation.
+For example, for a string or an array,
+it would be better to check if the returned value is the right type
+rather than casting which could lead to a fatal error.
+
+For a string that would give the following:
+```php
+$initial = 'my_value';
+
+$value = apply_filters('my_filter', $initial);
+
+if ( ! is_string( $value ) ) {
+    $value = $initial;
+}
+```
+
+#### Assert your callbacks value
+
+However, that incertitude on the type of the value inside filters does not only apply to their output, but it is also present on each callback.
+
+![Illustration from problem](./imgs/assert-callback-values.png)
+
+This is why it is important to never strongly type the value from a filter (the first parameter).
+
+The same way it is also important to always make a check on the type from the value before performing any operation on it.
+
+```php
+function my_callback($value) {
+    if(! is_string($value)) {
+        return $value;
+    }
+
+    return $value . "my_string";
+}
+```
+
+## Getting information on a hook
+
+Another good thing to know about hooks is how to get information about them.
+
+### Determining the current hook
+
+WordPress allows a callback function or method to be used on different events.
+
+Due to that, it can be sometimes unclear on which hook the callback is actually running.
+
+This is why WordPress introduced two functions.
+
+#### current_filter
+
+If you are in a callback linked with filters,
+it is possible to use the function [`current_filter`](https://developer.wordpress.org/reference/functions/current_filter/):
+
+```php
+function my_callback($value) {
+
+    if('the_content_feed' === current_filter()) {
+        return '';
+    }
+
+    return $value;
+}
+
+add_filter('the_content_rss', 'my_callback');
+add_filter('the_content_feed', 'my_callback');
+
+```
+
+#### current_action
+
+If you are in a callback linked with filters,
+it is possible to use the function [`current_action`](https://developer.wordpress.org/reference/functions/current_action/):
+
+```php
+function my_callback() {
+
+    if('init' === current_action()) {
+        return;
+    }
+
+    // my logic
+}
+
+add_filter('amin_init', 'my_callback');
+add_filter('init', 'my_callback');
+
+```
+### Check how many times a hook as run
+
+Sometimes it is important to know if a callback has already run to prevent it from running again.
+
+For that, it is possible to use two functions depending on if you want to check an action or a filter.
+
+#### did_filter
+
+If you want to know how many times a filter has been fired,
+you can use the [`did_filter`](https://developer.wordpress.org/reference/functions/did_filter/) function:
+
+```php
+function my_callback($value) {
+
+    if(0 < did_filter('pre_delete_attachment')) {
+        return $value;
+    }
+
+    // My logic
+
+    return $value;
+}
+
+add_filter('after_delete_post', 'my_callback');
+```
+
+#### did_action
+
+If you want to know how many times ana action has been fired,
+you can use the [`did_action`](https://developer.wordpress.org/reference/functions/did_action/) function:
+
+```php
+function my_callback() {
+
+    if(0 == did_action('amin_init')) {
+        return;
+    }
+
+    return ;
+
+    // my logic
+}
+
+add_action('added_option', 'my_callback');
+```