Backward Compatibility Practice with PHP

Backward Compatibility: Practice

Welcome back! Today, we'll master what we learned about backward compatibility in practice. Prepare to apply all the knowledge to practical tasks, but first, let's look at two examples and analyze them.

Task 1: Enhancing a Complex Data Processing Function with Optional Parameters and Default Values

Let's say that initially, we have a complex data processing class designed to operate on an array of associative arrays, applying a transformation that converts all string values within the array to uppercase. Here's the initial version using PHP: PHP<?php class DataProcessor { public function processData(array $items) { $processedItems = []; foreach ($items as $item) { $processedItem = []; foreach ($item as $key => $value) { if (is_string($value)) { $processedItem[$key] = strtoupper($value); } else { $processedItem[$key] = $value; } } $processedItems[] = $processedItem; } for ($i = 0; $i < min(3, count($processedItems)); $i++) { echo "Processed Item: "; print_r($processedItems[$i]); } } } We intend to expand this functionality, adding capabilities to filter the items based on a condition and allowing for custom transformations. The aim is to retain backward compatibility while introducing these enhancements. Here's the updated approach using optional parameters and closures: <?php class DataProcessor { public function processData(array $items, callable $condition = null, callable $transform = null) { if ($condition === null) { $condition = function ($item) { return true; }; } $processedItems = []; foreach ($items as $item) { if ($condition($item)) { $processedItem = []; if ($transform !== null) { $processedItem = $transform($item); } else { // Default transformation: Convert string values to uppercase foreach ($item as $key => $value) { $processedItem[$key] = is_string($value) ? strtoupper($value) : $value; } } $processedItems[] = $processedItem; } } for ($i = 0; $i < min(3, count($processedItems)); $i++) { echo "Processed Item: "; print_r($processedItems[$i]); } } } // Usage examples: $data = [ ["name" => "apple", "quantity" => 10], ["name" => "orange", "quantity" => 5] ]; $processor = new DataProcessor(); // Default behavior - convert string values to uppercase $processor->processData($data); // Custom filter - select items with a quantity greater than 5 $processor->processData($data, function ($item) { return $item['quantity'] > 5; }); // Custom transformation - convert names to uppercase and multiply the quantity by 2 $processor->processData($data, null, function ($item) { return [ 'name' => strtoupper($item['name']), 'quantity' => $item['quantity'] * 2 ]; }); In this evolved version, we've used optional parameters callable $condition and callable $transform for custom filtering and transformation of items. The default behavior processes all items, converting string values to uppercase, thus maintaining original functionality for existing code paths.

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PHP

<?php
class DataProcessor
{
    public function processData(array $items)
    {
        $processedItems = [];
        foreach ($items as $item) {
            $processedItem = [];
            foreach ($item as $key => $value) {
                if (is_string($value)) {
                    $processedItem[$key] = strtoupper($value);
                } else {
                    $processedItem[$key] = $value;
                }
            }
            $processedItems[] = $processedItem;
        }
        
        for ($i = 0; $i < min(3, count($processedItems)); $i++) {
            echo "Processed Item: ";
            print_r($processedItems[$i]);
        }
    }
}

PHP

<?php
class DataProcessor
{
    public function processData(array $items, callable $condition = null, callable $transform = null)
    {
        if ($condition === null) {
            $condition = function ($item) {
                return true;
            };
        }
        
        $processedItems = [];
        foreach ($items as $item) {
            if ($condition($item)) {
                $processedItem = [];
                
                if ($transform !== null) {
                    $processedItem = $transform($item);
                } else {
                    // Default transformation: Convert string values to uppercase
                    foreach ($item as $key => $value) {
                        $processedItem[$key] = is_string($value) ? strtoupper($value) : $value;
                    }
                }
                
                $processedItems[] = $processedItem;
            }
        }
        
        for ($i = 0; $i < min(3, count($processedItems)); $i++) {
            echo "Processed Item: ";
            print_r($processedItems[$i]);
        }
    }
}

// Usage examples:
$data = [
    ["name" => "apple", "quantity" => 10],
    ["name" => "orange", "quantity" => 5]
];

$processor = new DataProcessor();

// Default behavior - convert string values to uppercase
$processor->processData($data);

// Custom filter - select items with a quantity greater than 5
$processor->processData($data, function ($item) {
    return $item['quantity'] > 5;
});

// Custom transformation - convert names to uppercase and multiply the quantity by 2
$processor->processData($data, null, function ($item) {
    return [
        'name' => strtoupper($item['name']),
        'quantity' => $item['quantity'] * 2
    ];
});

<?php
class DataProcessor
{
    public function processData(array $items, callable $condition = null, callable $transform = null)
    {
        if ($condition === null) {
            $condition = function ($item) {
                return true;
            };
        }
        
        $processedItems = [];
        foreach ($items as $item) {
            if ($condition($item)) {
                $processedItem = [];
                
                if ($transform !== null) {
                    $processedItem = $transform($item);
                } else {
                    // Default transformation: Convert string values to uppercase
                    foreach ($item as $key => $value) {
                        $processedItem[$key] = is_string($value) ? strtoupper($value) : $value;
                    }
                }
                
                $processedItems[] = $processedItem;
            }
        }
        
        for ($i = 0; $i < min(3, count($processedItems)); $i++) {
            echo "Processed Item: ";
            print_r($processedItems[$i]);
        }
    }
}

// Usage examples:
$data = [
    ["name" => "apple", "quantity" => 10],
    ["name" => "orange", "quantity" => 5]
];

$processor = new DataProcessor();

// Default behavior - convert string values to uppercase
$processor->processData($data);

// Custom filter - select items with a quantity greater than 5
$processor->processData($data, function ($item) {
    return $item['quantity'] > 5;
});

// Custom transformation - convert names to uppercase and multiply the quantity by 2
$processor->processData($data, null, function ($item) {
    return [
        'name' => strtoupper($item['name']),
        'quantity' => $item['quantity'] * 2
    ];
});

PHP

<?php
class DataProcessor
{
    public function processData(array $items, callable $condition = null, callable $transform = null)
    {
        if ($condition === null) {
            $condition = function ($item) {
                return true;
            };
        }
        
        $processedItems = [];
        foreach ($items as $item) {
            if ($condition($item)) {
                $processedItem = [];
                
                if ($transform !== null) {
                    $processedItem = $transform($item);
                } else {
                    // Default transformation: Convert string values to uppercase
                    foreach ($item as $key => $value) {
                        $processedItem[$key] = is_string($value) ? strtoupper($value) : $value;
                    }
                }
                
                $processedItems[] = $processedItem;
            }
        }
        
        for ($i = 0; $i < min(3, count($processedItems)); $i++) {
            echo "Processed Item: ";
            print_r($processedItems[$i]);
        }
    }
}

// Usage examples:
$data = [
    ["name" => "apple", "quantity" => 10],
    ["name" => "orange", "quantity" => 5]
];

$processor = new DataProcessor();

// Default behavior - convert string values to uppercase
$processor->processData($data);

// Custom filter - select items with a quantity greater than 5
$processor->processData($data, function ($item) {
    return $item['quantity'] > 5;
});

// Custom transformation - convert names to uppercase and multiply the quantity by 2
$processor->processData($data, null, function ($item) {
    return [
        'name' => strtoupper($item['name']),
        'quantity' => $item['quantity'] * 2
    ];
});

PHP

<?php
class MusicPlayer
{
    public function play($file)
    {
        if (substr($file, -4) === '.mp3') {
            echo "Playing " . $file . " as mp3.\n";
        } else {
            echo "File format not supported.\n";
        }
    }
}

PHP

<?php
class MusicPlayerAdapter
{
    private $player;
    private $formatAdapters;
    
    public function __construct(MusicPlayer $player)
    {
        $this->player = $player;
        $this->formatAdapters = [
            '.wav' => function($file) {
                $convertedFile = str_replace('.wav', '.mp3', $file);
                echo "Converting $file to $convertedFile and playing as mp3...\n";
                $this->player->play($convertedFile);
            },
            '.flac' => function($file) {
                $convertedFile = str_replace('.flac', '.mp3', $file);
                echo "Converting $file to $convertedFile and playing as mp3...\n";
                $this->player->play($convertedFile);
            }
        ];
    }
    
    public function play($file)
    {
        $fileExtension = strtolower(pathinfo($file, PATHINFO_EXTENSION));
        $fileExtension = '.' . $fileExtension;
        
        if (isset($this->formatAdapters[$fileExtension])) {
            $this->formatAdapters[$fileExtension]($file);
        } else {
            $this->player->play($file);
        }
    }
}

// Upgraded music player with enhanced functionality through the composite adapter
$legacyPlayer = new MusicPlayer();
$enhancedPlayer = new MusicPlayerAdapter($legacyPlayer);

$enhancedPlayer->play("song.mp3");  // Supported directly
$enhancedPlayer->play("song.wav");  // Supported through adaptation
$enhancedPlayer->play("song.flac");  // Newly supported through additional adaptation

Backward Compatibility: Practice

Task 1: Enhancing a Complex Data Processing Function with Optional Parameters and Default Values

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Task 2: Using the Adapter Design Pattern for Backward Compatibility

Lesson Summary