<?php

function generate_result()
{
    echo "Result is being generated\n";
    return "result";
}

class Foo
{
    private $resultCache;

    public function getResult()
    {
        if (!isset($this->resultCache)) {
            $this->resultCache = generate_result();
        }

        return $this->resultCache;
    }
}

$obj = new Foo();

echo "Result is " . $obj->getResult() . "\n";
echo "Result is " . $obj->getResult() . "\n";
echo "Result is " . $obj->getResult() . "\n";

Result is being generated
Result is result
Result is result
Result is result