PHP 代码简洁之道(小结)(4)

日期：2020-05-15 栏目：程序人生浏览：次

函数应该只做一件事情

这是迄今为止软件工程最重要的原则。函数做了超过一件事情时，它们将变得难以编写、测试、推导。而函数只做一件事情时，重构起来则非常简单，同时代码阅读起来也非常清晰。掌握了这个原则，你就会领先许多其他的开发者。

不好的:

function emailClients(array $clients): void
{
 foreach ($clients as $client) {
  $clientRecord = $db->find($client);
  if ($clientRecord->isActive()) {
   email($client);
  }
 }
}

好的:

function emailClients(array $clients): void
{
 $activeClients = activeClients($clients);
 array_walk($activeClients, 'email');
}

function activeClients(array $clients): array
{
 return array_filter($clients, 'isClientActive');
}

function isClientActive(int $client): bool
{
 $clientRecord = $db->find($client);

 return $clientRecord->isActive();
}

函数的名称要说清楚它做什么

不好的例子:

class Email
{
 //...

 public function handle(): void
 {
  mail($this->to, $this->subject, $this->body);
 }
}

$message = new Email(...);
// What is this? A handle for the message? Are we writing to a file now?
$message->handle();

很好的例子:

class Email 
{
 //...

 public function send(): void
 {
  mail($this->to, $this->subject, $this->body);
 }
}

$message = new Email(...);
// Clear and obvious
$message->send();

函数只能是一个抽象级别

当你有多个抽象层次时，你的函数功能通常是做太多了。分割函数功能使得重用性和测试更加容易。.

不好:

function parseBetterJSAlternative(string $code): void
{
 $regexes = [
  // ...
 ];

 $statements = explode(' ', $code);
 $tokens = [];
 foreach ($regexes as $regex) {
  foreach ($statements as $statement) {
   // ...
  }
 }

 $ast = [];
 foreach ($tokens as $token) {
  // lex...
 }

 foreach ($ast as $node) {
  // parse...
 }
}

同样不是很好:

我们已经完成了一些功能，但是 parseBetterJSAlternative() 功能仍然非常复杂，测试起来也比较麻烦。

function tokenize(string $code): array
{
 $regexes = [
  // ...
 ];

 $statements = explode(' ', $code);
 $tokens = [];
 foreach ($regexes as $regex) {
  foreach ($statements as $statement) {
   $tokens[] = /* ... */;
  }
 }

 return $tokens;
}

function lexer(array $tokens): array
{
 $ast = [];
 foreach ($tokens as $token) {
  $ast[] = /* ... */;
 }

 return $ast;
}

function parseBetterJSAlternative(string $code): void
{
 $tokens = tokenize($code);
 $ast = lexer($tokens);
 foreach ($ast as $node) {
  // parse...
 }
}

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PHP 代码简洁之道(小结)(4)

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