Question

我想知道是否有办法限制施工中的价值。这是我的代码：

class Student : Human 
{
    private double Grade;

    public Student(string FirstName, string LastName, double Grade)
        : base(FirstName, LastName)
    {
        this.FirstName = FirstName;
        this.LastName = LastName;
        this.Grade = Grade;
    }
}

当我创建一个新学生时，我希望将等级限制在＆gt; = 2.00和＆lt; = 6.00之间，就像编译错误或运行时的异常一样。有办法吗？（不要担心其他字段FirstName和LastName）

Answer 1

您可以检查它并在运行时中抛出异常，如下所示：

if (grade < 2.00 || grade > 6.00) throw new ArgumentOutOfRangeException("grade");

始终将这些条件放在方法或构造函数的开头。我甚至将它们放在他们自己的#region中（但这是我个人的偏好）：

public Student(string firstName, string lastName, double grade) : base(firstName, lastName) { #region Contract if (grade < 2.00 || grade > 6.00) throw new ArgumentOutOfRangeException("grade"); #endregion this.FirstName = firstName; this.LastName = lastName; this.Grade = grade; }

但是，有一种方法可以使用代码约定来获取此类事件的编译时警告。您可以下载Code Contracts on MSDN，在那里您也可以找到文档。它仅与Visual Studio的非Express版本集成，由Microsoft编写。它将检查方法调用是否可能符合您指定的合同。您的代码将变为：

using System.Diagnotistics.Contracts; public Student(string firstName, string lastName, double grade) : base(firstName, lastName) { #region Contract Contract.Requires<ArgumentOutOfRangeException>(grade >= 2.00); Contract.Requires<ArgumentOutOfRangeException>(grade <= 6.00); #endregion this.FirstName = firstName; this.LastName = lastName; this.Grade = grade; }

Answer 2

你可以抛出异常：

class Student : Human 
{
    private double Grade;

    public Student(string FirstName, string LastName, double Grade)
        : base(FirstName, LastName)
    {
        if (Grade >= 2 && Grade <= 6) { 
          throw new ArgumentOutOfRangeException();
        }

        this.FirstName = FirstName;
        this.LastName = LastName;
        this.Grade = Grade;
    }
}

如果您正在使用Microsoft Code Contracts，那么您也可以这样做：

class Student : Human  {
    private double Grade;

    public Student(string FirstName, string LastName, double Grade)
        : base(FirstName, LastName)
    {
        System.Diagnotistics.Contracts.Contract.Requires<ArgumentOutOfRangeException>(Grade >= 2 && Grade <= 6);

        this.FirstName = FirstName;
        this.LastName = LastName;
        this.Grade = Grade;
    }
}

Answer 3

还有另一个选项，可能有点精简，但确保给定范围，根本不使用double，而是创建一个名为Grade的自定义类。您的Grade课程将包含来自double的演员表，并将强制执行验证。这意味着所有成绩验证逻辑都在Grade结构中，而Student类只接收Grade对象，而不必担心它。

public struct Grade
{
    public static readonly double MinValue = 2.0;
    public static readonly double MaxValue = 6.0;

    private double value;

    public static explicit operator double(Grade grade)
    {
        return grade.value + MinValue;
    }

    public static explicit operator Grade(double gradeValue)
    {
        if (gradeValue < MinValue || gradeValue > MaxValue)
            throw new ArgumentOutOfRangeException("gradeValue", "Grade must be between 2.0 and 6.0");

        return new Grade{ value = gradeValue - MinValue };
    }
}

你会像这样使用它：

double userInput = GetUserInputForGrade();
Grade grade = (Grade)userInput; // perform explicit cast.
Student student = new Student(firstName, lastName, grade);

编辑：我已使用@ EricLippert的建议更新了代码，以使该类向开发人员公开其最小/最大值。

编辑2：使用@ JeppeStigNielsen的建议再次更新。 value字段现在存储MinValue的偏移量，因此对default(Grade)的调用将返回有效值（等于MinValue），无论0是否在有效范围内。

Answer 4

class Student : Human 
{
    private double Grade;

    public Student(string FirstName, string LastName, double Grade)
        : base(FirstName, LastName)
    {
        if (Grade < 2 || Grade > 6)
            throw new ArgumentOutOfRangeException("Grade must be between 2 and 6");

        this.FirstName = FirstName;
        this.LastName = LastName;
        this.Grade = Grade;
    }
}

Answer 5

public Student(string FirstName, string LastName, double Grade)
    : base(FirstName, LastName)
    {
     if(Grade >= 2.0 || Grade <= 6.00)
      throw  new ArgumentException("your message");     
    }

Answer 6

如果你想要编译时间的任何机会，你必须使用代码合同。它们在运行时基本上是异常，因此等同于带有异常的参数验证。

public Student(string firstName, string lastName, decimal grade)
{
    Contract.Requires(grade >= 2);
    Contract.Requires(grade <= 6);

    FirstName = firstName;
    LastName = lastName;
    Grade = grade;     
}

看到这个问题

Design by contracts and constructors

Answer 7

class Student : Human 
{
    private double Grade;

    public Student(string FirstName, string LastName, double Grade)
        : base(FirstName, LastName)
    {
        this.FirstName = FirstName;
        this.LastName = LastName;
        this.Grade = Grade;
        if(Grade >= 2 and Grade <= 6){
            throw new Exception("Incorrect grade input");
    }
}

或者抛出你想要的相关例外，例如ArgumentOutOfrangeException等......

构造函数限制

7 个答案: