Type declarations in PHP7: how to avoid unexpected type errors?

Type declarations in PHP7: how to avoid unexpected type errors?

Introduction:
During the development process, type errors are one of the common causes of program malfunctions and runtime errors. To solve this problem, PHP7 introduced the feature of type declaration. This article will provide an in-depth introduction to the use of type declarations in PHP7 and how to avoid unexpected type errors through type declarations.

1. Overview of type declaration
The type declaration mechanism refers to declaring the expected data type on the parameters of a function or method. In PHP, type declarations can be applied to function or method parameters, return values, and class properties.

1. Examples of parameter type declarations for functions and methods:

   function add(int $a, int $b): int {
    return $a + $b;
   }

2. Examples of return value type declarations for functions and methods:

   function findUser(int $id): ?User {
    // 查询用户并返回 User 对象，如果找不到则返回 null
    // ...
   }

3. Example of type declaration of class attributes:

   class User {
    private int $id;
    private string $name;
   }

2. Benefits of enhancing code robustness
By using type declarations, code robustness can be effectively improved and maintainability, the specific benefits are as follows:

1. Stricter type checking: Type declaration can ensure that the incoming parameters and returned types meet expectations, avoiding potential type errors and resulting runtime abnormal.
2. Clearer code logic: Type declarations can clarify the input and output of functions or methods, making the code more readable and understandable, and better describing the meaning and requirements of the code.
3. Better code maintenance: Type declarations can help developers find errors earlier and provide better error prompts, thereby reducing the probability of errors and accelerating problem debugging and repair.

3. How to use type declarations

1. Scalar type declaration
   Scalar type declaration includes four basic types: int, float, string and bool . You can use scalar type declarations to define the types of parameters and return values ​​of functions or methods. Examples are as follows:

   function sum(int $a, int $b): int {
    return $a + $b;
   }

2. Class type declaration
   Class type declarations can be used for parameters and returns of functions or methods. Values ​​and attributes that specify a class or any of its subclasses that is expected as a type. An example is as follows:

function createProduct(string $name, int $price): Product {
    // 创建商品对象并返回
    // ...
}

3. NULL type declaration
   The NULL type declaration was introduced in PHP7 to specify that the parameter or return value can be null. Examples are as follows:

   function findUser(int $id): ?User {
    // 查询用户并返回 User 对象，如果找不到则返回 null
    // ...
   }

4. Notes on compatibility mode
By default, PHP7's type declaration is in strict mode, and the consistency of parameter types and return value types will be checked. Otherwise a TypeError will be thrown. However, if you need compatibility with older versions of PHP or want the flexibility of using type declarations in strict mode, consider using relaxed mode. Relaxed mode type declarations do not require strict type consistency and allow automatic type conversion.

You can use the declare(strict_types=0|1) program instruction at the top of the file to switch strict mode and relaxed mode. The example is as follows:

declare(strict_types=0); // 宽松模式
declare(strict_types=1); // 严格模式

5. Conclusion
Type declaration is introduced in PHP7 An important feature of type declaration is that it can avoid unexpected type errors, improve the quality and maintainability of code, and reduce runtime exceptions caused by type errors. During the development process, we should make reasonable use of type declarations and make type declarations for parameters and return values ​​of functions, methods, and attributes of classes, thereby improving the robustness and readability of the code. I hope this article can help everyone understand the type declaration and correct use in PHP7.

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