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English
The get_defined_constants function is one of the built-in functions of PHP, which is used to return all constants defined in the current script. It returns an associative array containing the constant name and its value. Through this function, developers can view defined constants anywhere in the program, making it easier to debug and analyze constant changes.
<?php
// Get all constants
$constants = get_defined_constants();
print_r($constants);
?>
The above code will return all defined constants and their corresponding values in the current script.
When Composer processes the project, it generates an autoload.php file based on the settings in the composer.json file. When we install dependency libraries through Composer, Composer will automatically load these dependency class files into the project. Composer's automatic loading mechanism automatically loads these class files by following the PSR-4 and PSR-0 standards, ensuring that all dependencies in the project can be correctly referenced.
The implementation of autoloading is usually to include the autoload.php file through the require_once or include_once statement. Composer loads corresponding class files and constants into the global scope, so developers may encounter constant changes when using these classes, especially when introducing new libraries or upgrading existing libraries.
Before and after Composer loads the dependency, we can use the get_defined_constants function to check for changes in constants. By comparing the list of constants before and after loading, we can see whether the newly introduced library or changed version defines a new constant, or changes the value of an existing constant.
Before the automatic loading of Composer, we can first obtain the list of constants in the current PHP script and save it:
<?php
// Get a list of constants before automatic loading
$before_constants = get_defined_constants();
print_r($before_constants);
?>
Next, run the Composer command to install the dependencies or update the project:
composer install
or
composer update
These commands trigger the automatic loading process of Composer, in which classes and constants in the dependency library will be loaded.
After the automatic loading of Composer is completed, get the current constant list again:
<?php
// Get the list of automatic loading constants
$after_constants = get_defined_constants();
print_r($after_constants);
?>
By comparing the $before_constants and $after_constants arrays, we can see which constants are newly introduced, or which have changed. For example, if a dependency library loaded by Composer defines a new constant, the constant will appear in the list of automatically loaded constants, and if a constant is modified, its value will also change.
<?php
// Get new constants
$new_constants = array_diff_key($after_constants, $before_constants);
print_r($new_constants);
?>
Through the above code, we can obtain the new constants added before and after the Composer automatically loads.
Changes in constants usually indicate that the library version has been updated or the configuration has been changed. Understanding these changes is very useful for debugging and updating projects during actual development. For example, when a library is updated, new constants may be introduced that affects the code in other parts of the project. If we can detect these changes in a timely manner through get_defined_constants , we can quickly identify potential problems and make appropriate adjustments.
Additionally, some libraries may define important configuration information in constants, such as database connection settings or API keys. If these constants change during the automatic loading process, we need to make sure that these changes do not affect the functionality of the project.
