Constructor restrictions

Question

i was wondering if there is a way to restrict a value in construction. Here is my code :

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;
    }
}

and when i make a new Student i want to restrict the Grade between >= 2.00 and <= 6.00 , like compile error or excepion on runtime. Is there a way ? (Don't worry about other fields FirstName, and LastName)

Answer 1

You can check it and throw an exception at runtime, like this:

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

Always put such conditions at the start of the method or constructor. I even put them in their own #region (but that's my personal preference):

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;
}

However, there is a way to get compile-time warnings for such things using Code Contracts. You can download Code Contracts on MSDN and there you can also find the documentation. It only integrates with non-Express versions of Visual Studio and is written by Microsoft. It will check whether method calls are likely to adhere to the contract you specify. Your code would then become:

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;
}