How to Properly Validate PHP Variable Types in WordPress

Summary

Introduction

Working with dynamic data is a core part of WordPress development. Functions frequently handle inputs from core features, plugins, APIs, or template files, and these inputs may not always be in the expected format. For instance, a filter could return an array when a string is expected. Without proper validation, such mismatches can lead to runtime errors, unpredictable behavior, or security issues. Type validation ensures that WordPress code executes safely and reliably.

Purpose of Validation

The main purpose of validation is to ensure that the data a function receives is in the expected format before processing it. By doing so, developers can:

• Avoid Runtime Errors: Functions can break if they receive unexpected input. Validation prevents these issues.
• Improve Compatibility: Plugins and themes often interact with third-party code. Validation ensures that external data does not break integration.
• Ensure Secure Execution: User inputs or REST API requests may be manipulated. Type validation protects against malicious or incorrect data.

function display_rating($rating) {
    if (!is_numeric($rating)) {
        $rating = 0; // fallback if rating is invalid
    }
    echo "Rating: " . $rating;
}

In this example, the function ensures $rating is numeric before using it, preventing errors if a string or array is accidentally passed.

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Why Type Checking is Important

Type checking is critical in WordPress development because:

1. Filters & Hooks Can Modify Data

WordPress filters can change the return values of functions unexpectedly.

$custom_title = apply_filters('custom_title_filter', get_the_title());
if (!is_string($custom_title)) {
    $custom_title = '';
}

Here, even though get_the_title() returns a string by default, a filter may alter it. Type checking prevents errors.

2. REST API & User Inputs

External inputs from forms or APIs may not follow the expected format.

$user_age = $_POST['age'];
if (!is_int($user_age)) {
    $user_age = intval($user_age); // safely convert to integer
}

3. Backward Compatibility

Some WordPress core functions return multiple types depending on context.

$meta = get_post_meta($post_id, 'custom_field', true);
if (!is_array($meta)) {
    $meta = array($meta); // ensure it is always treated as an array
}

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How Mandy Follows Validation in Every Project

At Mandy Technologies, variable type validation is a standard practice in all WordPress projects. Developers follow a structured approach to check the type of every input, ensuring:

• Consistent behaviour across plugins, themes, and custom functions.
• Reduced debugging and maintenance time.
• Safe handling of external and user-provided data.
• Reliable and predictable execution.

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Types of Checking and Examples

1. General PHP Type Checking

These functions validate standard PHP types:

• is_null($var) → Checks if a variable is NULL.

$value = null;
if (is_null($value)) {
    echo "Value is NULL";
}

• is_bool($var) → Checks if a variable is a boolean.

$flag = true;
if (is_bool($flag)) {
    echo "Flag is boolean";
}

• is_int($var) / is_integer($var) → Checks if a variable is an integer.

$age = 25;
if (is_int($age)) {
    echo "Age is integer";
}

• is_float($var) / is_double($var) → Checks if a variable is a float.

$price = 19.99;
if (is_float($price)) {
    echo "Price is float";
}

• is_numeric($var) → Checks if a variable is numeric.

$value = "100";
if (is_numeric($value)) {
    echo "Value is numeric";
}

• is_string($var) → Checks if a variable is a string.

$name = "Mandy Technologies";
if (is_string($name)) {
    echo "Name is string";
}

• is_array($var) → Checks if a variable is an array.

$items = array('apple', 'banana');
if (is_array($items)) {
    echo "Items is array";
}

• is_object($var) → Checks if a variable is an object.

$obj = new stdClass();
if (is_object($obj)) {
    echo "Variable is object";
}

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2. WordPress-Specific Type Checking

WordPress provides additional functions for common object types:

• is_wp_error($var) → Checks if a variable is a WP_Error object.

$result = wp_insert_post($post_data);
if (is_wp_error($result)) {
    echo "Error inserting post: " . $result->get_error_message();
}

• is_a($var, ‘WP_Post’) → Checks if a variable is a WP_Post object.

$post = get_post($post_id);
if (is_a($post, 'WP_Post')) {
    echo $post->post_title;
}

• is_a($var, ‘WP_User’) → Checks if a variable is a WP_User object.

$user = wp_get_current_user();
if (is_a($user, 'WP_User')) {
    echo "User ID: " . $user->ID;
}

• is_a($var, ‘WP_Term’) → Checks if a variable is a WP_Term object.

$term = get_term($term_id);
if (is_a($term, 'WP_Term')) {
    echo "Term Name: " . $term->name;
}

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3. Debugging Helpers

These functions help inspect variables and debug type-related issues:

• gettype($var) → Returns the type of the variable as a string.

$value = "Hello";
echo gettype($value); // Output: string

• var_dump($var) → Outputs type and value for debugging.

$items = array('apple', 'banana');
var_dump($items);

• print_r($var, true) → Returns a readable value of the variable.

$items = array('apple', 'banana');
echo print_r($items, true);

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Common Questions About PHP Type Validation

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Conclusion

PHP variable type validation is a critical practice in WordPress development. It helps prevent runtime errors, ensures compatibility, and improves code security. By using general PHP checks, WordPress-specific functions, and debugging helpers, developers at Mandy Technologies maintain high-quality standards, handle unexpected inputs gracefully, and deliver reliable, predictable, and secure WordPress projects.

Have questions or need help building your WordPress site? Reach out to us today and get expert guidance!