Scalar type declarations in PHP7: How to increase code reliability and maintainability?

The scalar type declaration feature was introduced in PHP7, which allows developers to specify explicit data types on function parameters and return values. This feature can not only enhance the reliability of the code, but also improve the maintainability of the code. This article will introduce the use of scalar type declarations in PHP7 and give some specific code examples.

Before PHP7, PHP was a dynamically typed language, that is, the data type of variables was automatically determined based on assignment. This flexibility is good for some scenarios, but it can also cause some problems. For example, in a function, if the type of parameters is not verified, passing in an incorrect data type may cause unexpected errors.

The scalar type declaration in PHP7 can specify four scalar types for function parameters and return values: int (integer), float (floating point number), string (string) and bool (Boolean value). Using scalar type declarations allows developers to handle data types more clearly and confidently when writing functions, avoiding some common mistakes.

The following is an example of a function declared using a scalar type:

function multiply(int $a, int $b): int {
    return $a * $b;
}

echo multiply(5, 10); // 输出 50
echo multiply(5, '10'); // 报错：Argument 2 must be of the type integer, string given

In the above example, the two parameters and return value of the multiply function are declared as int type. When we pass in two integers, the function executes normally and returns the correct result. But when we pass in an integer and a string, the PHP interpreter will report an error, telling us that the second parameter must be of integer type. This avoids the need to operate on non-integer type parameters inside the function, thereby ensuring that the behavior of the function is reliable.

In addition to the above basic types, some special types can also be used for more precise type constraints. For example, you can use the bool type to only allow function parameters to be boolean:

function isAdult(bool $isAdult): string {
    if ($isAdult) {
        return '成年人';
    } else {
        return '未成年人';
    }
}

echo isAdult(true); // 输出 成年人
echo isAdult(1); // 输出 成年人
echo isAdult(false); // 输出 未成年人
echo isAdult(0); // 输出 未成年人

In the above example, the parameters of the isAdult function are declared as bool type, and the return value is declared as string type. This ensures that the parameters of the function can only be boolean values, and the return value of the function can only be of string type.

Scalar type declarations are not only valid on function parameters, but can also be used on function return values. This makes it clearer when calling a function the data type of the return value. For example:

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

echo divide(10, 2); // 输出 5.0（浮点数）
echo divide(10, 3); // 输出 3.3333333333333（浮点数）

In the above example, the parameters and return value of the divide function are declared as int and float types. Even if the result of the division operation is a floating point number, the return value of the function can be specified as a float type. This can help us better understand the behavior of the function and process the results accurately when needed.

It should be noted that the scalar type declaration does not force checking whether the variable conforms to the specified type. But when using traditional weak type judgment, if the data types do not match, forced conversion will be automatically performed. Therefore, it is still up to the developer to ensure that the data type of the variable is correct.

By using scalar type declarations in PHP7, you can make your code more explicit and reliable. It helps developers find errors that may occur when passing parameters and makes it easier to maintain and understand the code. Although scalar type declaration is not mandatory, it is a good practice for developing high-quality PHP code.

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