Scalar type declarations in PHP7: How to prevent common type errors?

Scalar type declarations in PHP7: How to prevent common type errors?

In PHP7, scalar type declarations are introduced, which is a new feature that allows you to specify the expected data type in the position of function and method parameters and return values. This is very helpful for avoiding common type errors. This article will use specific code examples to introduce how to use scalar type declarations to prevent these errors.

1. Parameter type declaration

Before PHP7, we could not impose type constraints on the parameters of functions or methods. This resulted in some unexpected errors during parameter passing. But in PHP7, we can specify the expected type of a parameter by prepending the data type before the parameter name.

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

In the above code, we use int to type declare the parameters $a and $b as integer types. In the function body, when the incoming parameter is not an integer type, PHP will automatically try to perform type conversion. If the conversion cannot be performed, a fatal error will be thrown. In this way, we can find errors during the development process and fix them in time.

2. Return value type declaration

Before PHP7, the return value type of a function or method could only be described through comments or documents, which made the code less readable. But in PHP7, we can directly specify the data type of the return value in the definition of the function or method.

function divide(float $a, float $b): float {
    return $a / $b;
}

In the above code, we use float to specify the type of return value as a floating point number. Within the function body, if the type of the return value does not match the declared type, PHP will throw a fatal error. In this way, we can detect these types of errors in time during the coding process.

3. Nullable parameters and return values

In PHP7, we can also use ? to indicate that parameters or return values ​​can be null. This is very useful for designing certain optional parameters or return values.

function findUser(?int $id): ?string {
    // 根据id查找用户
    if ($user) {
        return $user->name;
    } else {
        return null;
    }
}

In the above code, we use ?int to indicate that the $id parameter can be empty, and use ?string to indicate that the return value can be Is empty. In this way, we can clearly express these optional options in the definition of the function or method, and handle them accordingly when calling.

4. Type conversion

When using a scalar type declaration, if the incoming parameter cannot be type converted, PHP will try to perform automatic conversion. If it still fails, a type will be thrown mistake. For example, when a string is passed to a parameter declared of type integer, PHP will try to convert it to an integer, but will throw a type error if the string cannot be converted to an integer.

function printAge(int $age) {
    echo "年龄：" . $age;
}

printAge("20岁")； // 抛出类型错误，无法将字符串转换为整数

By using scalar type declarations, we can prevent such type errors, improve code quality and improve program maintainability.

Summary:

In PHP7, we can use scalar type declarations to prevent common type errors. By imposing type constraints on the parameters and return values ​​of functions and methods, we can find and fix these errors in time during the coding process. At the same time, optional parameters and return values ​​can be handled gracefully using nullable parameters and return values. You need to pay attention to type conversion issues when using it, and ensure that the type declaration can successfully convert the incoming parameters.

Although scalar type declarations have been introduced in PHP7, they are not mandatory. We can still not use scalar type declarations in our code. However, using it can improve code quality and readability and reduce error rates during development, so it is recommended to use scalar type declarations where appropriate.

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