php函数的必选参数混淆 [英] php function's required parameter confusion

问题描述

我正在 PHP 函数签名中寻找 必需参数 的确切类型

I am looking for the exact type of a Required Parameter in a PHP Function signature

仅使用 NULL 初始化参数是否使其成为可选参数?即

Does initializing a parameter only with NULL makes it an optional? i.e

function foo($optional=NULL, $OptionalOrRequired="Optional Or Required", $required){}

我对第二个参数感到困惑，它是必需参数还是可选参数?

I am confused about the 2nd argument, does it comes in Required or Optional parameter?

更新

我正在使用 reflection 来获取函数的所有和必需的参数

I am using reflection to get all and required parameters of a function

public function getPlayer($params=3, $c){}
// results
$reflection->getNumberOfParameters()            ->   2
$reflection->getNumberOfRequiredParameters()    ->   2 // it should be one

public function getPlayer($params=3, $c, $x=NULL)
// results
$reflection->getNumberOfParameters()            ->   3
$reflection->getNumberOfRequiredParameters()    ->   2

当我得到一个默认值在需要之前的答案时，这是否是反射函数为所需参数返回错误计数的原因?

As i get in one answer that defaults comes before required, is this the reason the reflection function is returning wrong count for required parameters?

谢谢

推荐答案

'Optional' arguments 只是带有默认值的参数，该值是否为 null, false, 字符串(等)无关紧要 - 如果函数参数具有默认值，则它是可选的.

'Optional' arguments are just arguments with a default value, whether that value is null, false, a string (etc.) does not matter - if a function argument has a default value it is optional.

但是，在必需参数之前放置一个可选参数是没有意义的，因为您必须为前面的参数赋予一些值(即使它是 null)才能到达' 必需的参数 - 所以最后一个 'required' 参数之前的所有参数都是有效的.

However, it wouldn't make sense to have an optional parameter come before a required parameter, as you must give the prior arguments some value (even if it's null) in order to 'get to' the required argument - so all arguments before the last 'required' argument are effectively required.

一些例子:

// Bad
function bad($optional = 'literally anything', $required) {}

bad('required arg');              // This breaks - 'missing argument 2'
bad('something', 'required arg'); // This works - both parameters are needed

// Good
function($required, $optional = 'literally anything') {}

good('required arg');              // This works just fine, last argument has a default
good('required arg', 'something'); // Also works fine, overrides 'literally anything'

更新 RE:反思

如上所述，将可选"参数放在必需参数之前有效地使可选"参数成为必需，因为必须为其指定值才能满足方法签名.

As noted above, putting an 'optional' parameter before a required parameter effectively makes that 'optional' parameter required, as a value must be given for it in order to ever satisfy the method signature.

例如，如果第一个参数有默认值而第二个参数没有(如上面的 bad 函数)，我们需要传递第二个参数，因此我们需要传递第一个参数也有论点，所以两者都是必需的".如果后续参数有默认值，仍然只需要前2个参数.

For example, if the first argument has a default and second argument does not (like in the bad function above), we NEED to pass a second argument, and so we NEED to pass a first argument also, so both are 'required'. If there are subsequent arguments with default values, still only the first 2 arguments are required.

这篇关于php函数的必选参数混淆的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！