PHP 8.1引入了交集類型，使用&運(yùn)算符指定值必須同時(shí)滿足多個(gè)類型約束。1. 交集類型用于函數(shù)參數(shù)時(shí)確保對象實(shí)現(xiàn)多個(gè)接口，如function example(FooInterface & BarInterface $param)。2. 使用場景包括設(shè)計(jì)需要組合能力的API或庫、與mixin和trait結(jié)合時(shí)增強(qiáng)類型安全性。3. 實(shí)踐建議：僅用于對象類型、變量命名應(yīng)清晰表達(dá)組合類型含義、避免過度嵌套使用。4. 現(xiàn)代IDE和靜態(tài)分析工具如PHPStan已良好支持該特性。5. 注意交集類型要求對象必須完整實(shí)現(xiàn)所有指定接口，與聯(lián)合類型不同且更嚴(yán)格。

In PHP 8.1, intersection types allow you to specify that a value must satisfy multiple type constraints at the same time. While union types (using |) let you accept one of several types, intersection types (using &) require a value to be all of the specified types simultaneously.

This can be particularly useful for function parameters when you need an object that implements multiple interfaces or combines traits. Here's how you can use them effectively.

Understanding Intersection Types

Intersection types are written using the & operator. For example:

function example(FooInterface & BarInterface $param): void {
    // $param must implement both FooInterface and BarInterface
}

Before PHP 8.1, there was no native way to enforce this behavior directly in type declarations — you’d have to check manually inside the function body. Now, it’s enforced at the type level.

This is especially helpful when working with complex systems where objects need to conform to multiple contracts.

When to Use Them for Function Parameters

You should consider using intersection types when:

• You want to ensure an object satisfies multiple interface requirements.
• You're designing APIs or libraries that expect combined capabilities from input objects.
• You’re working with mixins or trait-based designs and want stricter typing.

For instance, imagine you have two interfaces: LoggerInterface and SerializableInterface. If a function needs an object that can both log and be serialized, you can now write:

function process(LoggerInterface & SerializableInterface $handler): void {
    $handler->log('Started processing');
    file_put_contents('data.txt', serialize($handler));
}

This makes your expectations clear and avoids runtime surprises.

Practical Tips for Using Intersection Types

Here are some things to keep in mind:

• Interfaces only – Intersection types currently work only with object types (not scalar types like int or string).
• Order doesn’t matter – A & B is the same as B & A.
• Use descriptive variable names – Since the type already shows what’s expected, naming the parameter something like $loggerAndSerializer helps readability.
• Avoid overuse – Intersection types are powerful but can make code harder to read if overused or nested deeply.

Also, remember that the passed object must actually fulfill all the required interfaces — just implementing one won't be enough.

Compatibility and Tooling Support

As of PHP 8.1 , most modern IDEs (like PhpStorm, VS Code with appropriate extensions) understand intersection types and will provide auto-completion and error checking. Static analysis tools such as PHPStan and Psalm also support them well.

If you're upgrading older code or working in a team, make sure everyone knows that intersection types are stricter than union types and serve a different purpose.

So, when writing functions that expect highly specialized objects, intersection types help you express those expectations clearly and safely. It's not complicated, but it does require thinking carefully about your object design.

基本上就這些。

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