condition orientated programming • Jr. StrangeDev

練習 smart contract 的時候，看到 function modifiers 很有趣，所以又稱為 condition orientated programming，其精神在於讓 condition 可以重用，而且讓你的 function 內不會有太多的 if statement

所以後來思考了一下， php 應該也可以做到像是這樣的事情，所以才有了下面的 sample code

<?php
interface Condition
{
    public function assert(...$rule);
}

trait Operator
{
    public function greatThan($left, $right)
    {
        return $left > $right;
    }
}

class Vip implements Condition
{
    public function assert(...$rule)
    {
        list($isVip) = $rule;
        return ('yes' == $isVip) ? true : false;
    }
}

class Money implements Condition
{
    use Operator;

    public function assert(...$rule)
    {
        list($money, $operator, $integer) = $rule;
        return call_user_func([$this, $operator], $money, $integer);
    }
}

class Judgement
{
    public $conditionList = [];
    public $status;

    public function condition(Condition $condition)
    {
        $reflect  = new ReflectionClass($condition);
        $instanceName = $reflect->getShortName();
        $this->conditionList[$instanceName] = $condition;
    }

    public function judge(Array $rules)
    {
        $result = true;

        foreach ($this->conditionList as $instance) {
            $reflect  = new ReflectionClass($instance);
            $instanceName = $reflect->getShortName();
            $parameters = $rules[$instanceName];

            $result = $result && call_user_func([$instance, 'assert'], ...$parameters);
        }
        $this->status = $result;
        return $this;
    }

    public function then(Closure $callback)
    {
        return (true === $this->status) ? $callback() : false;
    }
}


class User
{
    public $money = 10;
    public $isVip = 'yes';
}

// start your code
$user = new User;

$vipUserRule = new Judgement;
$vipUserRule->condition(new Vip);
$vipUserRule->condition(new Money);

$bonus = $vipUserRule
    ->judge([
        'Vip' => [$user->isVip],
        'Money' => [$user->money, 'greatThan', '50']
    ])
    ->then(function () use ($user) {
        return $bonus = $user->money * 0.9 + 99;
    });

var_export($bonus);
echo PHP_EOL;

其實還蠻有趣的，雖然上面的程式碼等價下面的程式碼

class User
{
    public $money = 10;
    public $isVip = 'yes';
}

// start your code
$user = new User;
$bonus = false;
if ($user->isVip && $user->money > 50) {
    $bonus = $user->money * 0.9 + 99;
}

var_export($bonus);
echo PHP_EOL;

Why?

那為什麼要寫得這麼複雜呢？其實不外乎有：

condition 的重用這些 condition 是可以重複使用的，而且直覺，可以輕易的修改 condition 的內容
專注 function 在你的 anonymous function 裡不會有任何 if statement，這樣就可以更容易知道這個 function 到底要做什麼事情

so, 就是個練習 :p