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清单 6. 良好习惯：带注释的函数和类
处理错误
根据大众的经验，如果要编写健壮的应用程序，错误处理要遵循 80/20 规则：80% 的代码用于处理异常和验证，20% 的代码用于完成实际工作。在编写程序的基本逻辑（happy-path）代码时经常这样做。这意味着编写适用于基本条件的代码，即所有的数据都是可用的，所有的条件符合预期。这样的代码在应用程序的生命周期中可能很脆弱。另一个极端是，甚至需要花大量时间为从未遇到过的条件编写代码。
这一习惯要求您编写足够的错误处理代码，而不是编写对付所有错误的代码，以致代码迟迟不能完成。
不良习惯：根本没有错误处理代码
清单 7 中的代码演示了两个不良习惯。第一，没有检查输入的参数，即使知道处于某些状态的参数会造成方法出现异常。第二，代码调用一个可能抛出异常的方法，但没有处理该异常。当发生问题时，代码的作者或维护该代码的人员只能猜测问题的根源。
清单 7. 不良习惯：不处理错误条件
＜?php
// Get the actual name of the
function convertDayOfWeekToName($day)
{
$dayNames = array(
"Sunday",
"Monday",
"Tuesday",
"Wednesday",
"Thursday",
"Friday",
"Saturday");
return $dayNames[$day];
}
echo("The name of the 0 day is: " . convertDayOfWeekToName(0) . "n");
echo("The name of the 10 day is: " . convertDayOfWeekToName(10) . "n");
echo("The name of the 'orange' day is: " . convertDayOfWeekToName('orange') . "n");
?＞
清单 8 展示了以有意义的方式抛出和处理异常。额外的错误处理不仅使代码更加健壮，它还提高代码的可读性，使代码更容易理解。处理异常的方式很好地说明了原作者在编写方法时的意图。
清单 8. 良好习惯：处理异常
虽然检查参数是一种确认 — 如果您要求参数处于某种状态，这将对使用方法的人很有帮助 — 但是您应该检查它们并抛出有意义的异常：
◆处理异常要尽量与出现的问题紧密相关。
◆专门处理每个异常。
切忌使用复制粘贴
您可以从其他地方将代码复制粘贴到自己的代码编辑器，但这样做有利也有弊。好的一面是，从一个示例或模板中复制代码能够避免很多错误。不好的一面是，这容易带来大量的类似编程方式。
一定要注意，不要将代码从应用程序的一部分复制粘贴到另一部分。如果您采用这种方式，请停止这个不良的习惯，然后考虑将这段代码重写为可重用的。一般而言，将代码放置到一个地方便于日后的维护，因为这样只需在一个地方更改代码。
不良习惯：类似的代码段
清单 9 给出了几个几乎一样的方法，只是其中的值不同而已。有一些工具可以帮助找到复制粘贴过来的代码（参见 参考资料）。
清单 9. 不良习惯：类似的代码段
良好习惯：带参数的可重用函数
清单 10 展示了修改后的代码，它将复制的代码放到一个方法中。另一个方法也进行了更改，它现在将任务委托给新的方法。构建通用的方法需要花时间设计，并且这样做使您能停下来思考，而不是本能地使用复制粘贴。但有必要进行更改时，对通用的方法投入的时间将得到回报。
清单 10. 良好习惯：带参数的可重用函数
结束语
如果您在编写 PHP 代码的过程中养成本文讨论的良好习惯，您将能够构建易读、易理解、易维护的代码。使用这种方式构建的易维护代码将降低调试、修复和扩展代码所面临的风险。
使用良好的名称和更短的方法能够提高代码的可读性。注释代码的目的有利于代码理解和扩展。适当地处理错误会使代码更加健壮。最后，停止使用复制粘贴，保持代码干净，提高可重用性。
＜?php
/*
* Counts the messages with the given severity in the array
* of messages.
*
* @param $messages An array of ResultMessage
* @return int Count of messages matching $withSeverity
*/
function countMessages($messages, $withSeverity)
{
$matchingCount = 0;
foreach($messages as $m) {
if ($m-＞getSeverity() == $withSeverity) {
$matchingCount++;
}
}
return $matchingCount;
}
/**
* Counts the number of messages found in the array of
* ResultMessage with the getSeverity() value of "Error"
*
* @param $messages An array of ResultMessage
* @return unknown_type
*/
function countErrors($messages)
{
return countMessages($messages, "Errors");
}
/**
* Counts the number of messages found in the array of
* ResultMessage with the getSeverity() value of "Warning"
*
* @param $messages An array of ResultMessage
* @return unknown_type
*/
function countWarnings($messages)
{
return countMessages($messages, "Warning");
}
/**
* Counts the number of messages found in the array of
* ResultMessage with the getSeverity() value of "Warning"
*
* @param $messages An array of ResultMessage
* @return unknown_type
*/
function countInformation($messages)
{
return countMessages($messages, "Information");
}
$messages = array(new ResultMessage("Error", "This is an error!"),
new ResultMessage("Warning", "This is a warning!"),
new ResultMessage("Error", "This is another error!"));
$errs = countErrors($messages);
echo("There are " . $errs . " errors in the result.n");
?＞
＜?php
/**
* Counts the number of messages found in the array of
* ResultMessage with the getSeverity() value of "Error"
*
* @param $messages An array of ResultMessage
* @return unknown_type
*/
function countErrors($messages)
{
$matchingCount = 0;
foreach($messages as $m) {
if ($m-＞getSeverity() == "Error") {
$matchingCount++;
}
}
return $matchingCount;
}
/**
* Counts the number of messages found in the array of
* ResultMessage with the getSeverity() value of "Warning"
*
* @param $messages An array of ResultMessage
* @return unknown_type
*/
function countWarnings($messages)
{
$matchingCount = 0;
foreach($messages as $m) {
if ($m-＞getSeverity() == "Warning") {
$matchingCount++;
}
}
return $matchingCount;
}
/**
* Counts the number of messages found in the array of
* ResultMessage with the getSeverity() value of "Information"
*
* @param $messages An array of ResultMessage
* @return unknown_type
*/
function countInformation($messages)
{
$matchingCount = 0;
foreach($messages as $m) {
if ($m-＞getSeverity() == "Information") {
$matchingCount++;
}
}
return $matchingCount;
}
$messages = array(new ResultMessage("Error", "This is an error!"),
new ResultMessage("Warning", "This is a warning!"),
new ResultMessage("Error", "This is another error!"));
$errs = countErrors($messages);
echo("There are " . $errs . " errors in the result.n");
?＞
＜?php
/**
* This is the exception thrown if the day of the week is invalid.
* @author nagood
*
*/
class InvalidDayOfWeekException extends Exception { }
class InvalidDayFormatException extends Exception { }
/**
* Gets the name of the day given the day in the week. Will
* return an error if the value supplied is out of range.
*
* @param $day
* @return unknown_type
*/
function convertDayOfWeekToName($day)
{
if (! is_numeric($day)) {
throw new InvalidDayFormatException('The value '' . $day . '' is an ' .
'invalid format for a day of week.');
}
if (($day ＞ 6) || ($day ＜ 0)) {
throw new InvalidDayOfWeekException('The day number '' . $day . '' is an ' .
'invalid day of the week. Expecting 0-6.');
}
$dayNames = array(
"Sunday",
"Monday",
"Tuesday",
"Wednesday",
"Thursday",
"Friday",
"Saturday");
return $dayNames[$day];
}
echo("The name of the 0 day is: " . convertDayOfWeekToName(0) . "n");
try {
echo("The name of the 10 day is: " . convertDayOfWeekToName(10) . "n");
} catch (InvalidDayOfWeekException $e) {
echo ("Encountered error while trying to convert value: " . $e-＞getMessage() . "n");
}
try {
echo("The name of the 'orange' day is: " . convertDayOfWeekToName('orange') . "n");
} catch (InvalidDayFormatException $e) {
echo ("Encountered error while trying to convert value: " . $e-＞getMessage() . "n");
}
?＞
良好习惯：处理异常
＜?php
/**
* The ResultMessage class holds a message that can be returned
* as a result of a process. The message has a severity and
* message.
*
* @author nagood
*
*/
class ResultMessage
{
private $severity;
private $message;
/**
* Constructor for the ResultMessage that allows you to assign
* severity and message.
* @param $sev See {@link getSeverity()}
* @param $msg
* @return unknown_type
*/
public function __construct($sev, $msg)
{
$this-＞severity = $sev;
$this-＞message = $msg;
}
/**
* Returns the severity of the message. Should be one
* "Information", "Warning", or "Error".
* @return string Message severity
*/
public function getSeverity()
{
return $this-＞severity;
}
/**
* Sets the severity of the message
* @param $severity
* @return void
*/
public function setSeverity($severity)
{
$this-＞severity = $severity;
}
public function getMessage()
{
return $this-＞message;
}
public function setMessage($msg)
{
$this-＞message = $msg;
}
}
/*
* Counts the messages with the given severity in the array
* of messages.
*
* @param $messages An array of ResultMessage
* @return int Count of messages with a severity of "Error"
*/
function countErrors($messages)
{
$matchingCount = 0;
foreach($messages as $m) {
if ($m-＞getSeverity() == "Error") {
$matchingCount++;
}
}
return $matchingCount;
}
$messages = array(new ResultMessage("Error", "This is an error!"),
new ResultMessage("Warning", "This is a warning!"),
new ResultMessage("Error", "This is another error!"));
$errs = countErrors($messages);
echo("There are " . $errs . " errors in the result.n");
?＞
＜?php
class ResultMessage
{
private $severity;
private $message;
public function __construct($sev, $msg)
{
$this-＞severity = $sev;
$this-＞message = $msg;
}
public function getSeverity()
{
return $this-＞severity;
}
public function setSeverity($severity)
{
$this-＞severity = $severity;
}
public function getMessage()
{
return $this-＞message;
}
public function setMessage($msg)
{
$this-＞message = $msg;
}
}
function cntMsgs($messages)
{
$n = 0;
/* iterate through the messages... */
foreach($messages as $m) {
if ($m-＞getSeverity() == 'Error') {
$n++; // add one to the result;
}
}
return $n;
}
$messages = array(new ResultMessage("Error", "This is an error!"),
new ResultMessage("Warning", "This is a warning!"),
new ResultMessage("Error", "This is another error!"));
$errs = cntMsgs($messages);
echo("There are " . $errs . " errors in the result.n");
?＞
将长方法拆分为短方法也是有限制的，过度拆分将适得其反。因此，不要滥用这个良好的习惯。将代码分成大量的片段就像没有拆分长代码一样，都会造成阅读困难。
如果多编写几个这样的方法，维护就成了真正的难题了。良好习惯：说明性强并且简洁的名称
(责任编辑：admin) |
