Use array_diff_key() to find newly added constants

PHP provides the get_defined_constants() function, which can return all defined constants in the current script. The function returns an associative array where the key is the name of the constant and the value is the value of the constant. For example:

 $constants = get_defined_constants();
print_r($constants);

This code will output all defined constants and their values. Suppose we have two versions of constant definition list: one is the old version of the constant definition and the other is the new version of the constant definition.

2. Comparison of the two versions of constants

Suppose we have two constant arrays, one is the old version of the constant and the other is the new version of the constant. We can find the new constants added in the new version through the array_diff_key() function. The array_diff_key() function can compare the keys (i.e. constant names) of two arrays, returning key-value pairs that are in the first array but not in the second array.

 // Old version of constants
$old_constants = get_defined_constants();

// Simulate the new version of constants
define('NEW_CONSTANT', 'New Value');
define('ANOTHER_NEW_CONSTANT', 'Another New Value');
$new_constants = get_defined_constants();

// use array_diff_key Find new constants
$new_added_constants = array_diff_key($new_constants, $old_constants);

// Output new constants
print_r($new_added_constants);

3. Parsing the code

In this example, first use get_defined_constants() to get all defined constants in the current script. Then, simulate a new version of the constant definition and call get_defined_constants() again to get the new constant list. Compare the array of new and old constants through the array_diff_key() function to find the newly added constants.

array_diff_key() compares the keys of the two arrays, returning the part of the key (constant name) in the new array that does not exist in the old array. Ultimately, this way we can find out the newly added constants.

4. Practical application

This approach is very useful for comparing different versions of constants in large projects. Especially in a multi-person collaboration development environment, tracking newly added constants can help developers quickly understand the updated content of the project and avoid errors caused by constant name conflicts or omissions.

5. Things to note

• get_defined_constants() will only return constants defined in the current script, so when using this method, make sure the list of constants you get is up to date.

• array_diff_key() only compares the key names of the array. If the value of the constant changes but the key names do not change, this method cannot detect.

• If you need to view the value of a specific constant, get_defined_constants() returns an array containing the constant name and the constant value, and its value can be accessed directly through the constant name.

In this way, you can easily find the constants added in the new version, ensuring that the code is updated and maintained more efficiently.