transform_demo.php

<?php

class BalanceSheet
{
    public function __construct(public int $liabilities, public int $equity)
    {
    }
}

class AssetsCalculator
{
    public function calculateAssets(BalanceSheet $balanceSheet): int
    {
        return $balanceSheet->liabilities + $balanceSheet->equity;
    }
}

$assetsCalculator = new AssetsCalculator();

/**
 * The following is the different way to achieve the same result as in transform-demo.clj.
 * In OOP, we first create an empty collection structure (an empty vector, list or array in PHP) and when we mutate it
 * by adding elements to it.
 */
$assetList = [];
foreach (
    [
        '1950' => new BalanceSheet(7000, 15000),
        '1951' => new BalanceSheet(14000, 100000),
        '1953' => new BalanceSheet(45000, 350000),
    ] as $year => $sheet
) {
    $assetList[] = $assetsCalculator->calculateAssets($sheet);
}

echo join(', ', $assetList) . PHP_EOL;
# 22000, 114000, 395000