c# generics - need help

Question

For the example on the code below which of the following statements are true? public class MyContainer where T: class IComparable { //Insert code here } I. MyContainer class demands that the generic parameter implements IComparable interface. II. The compiler will report an error for that code block.-False III. There are multiple constraints on MyContainer generic parameter definition. -True IV. MyContainer class demands that the generic parameter is of reference type and also implements the IComparable interface. - True a) I and II only b) I III and IV only c) II and III only d) All above e) None of the above

Dhirendra Misra · Answer

Hello The statements III and IV are true. The statement 1 is not true as it explains incomplete behaviour. You can try using following examples: class genericClass where T: class IComparable { public void somemethod(T t) { Console.Write(t.ToString()); Console.Read(); } } class Employee : IComparable { public int Salary { get; set; } public string Name { get; set; } public int CompareTo(object other) { Employee emp = (Employee)other; // Alphabetic sort if salary is equal. [A to Z] if (this.Salary == emp.Salary) { return this.Name.CompareTo(emp.Name); } // Default to salary sort. [High to low] return emp.Salary.CompareTo(this.Salary); } public override string ToString() { // String representation. return this.Salary.ToString() +  + this.Name; } } class EmployeeWithoutIComparable { public int Salary { get; set; } public string Name { get; set; } } struct EmployeeStruct : IComparable { public int Salary { get; set; } public string Name { get; set; } public int CompareTo(object other) { Employee emp = (Employee)other; // Alphabetic sort if salary is equal. [A to Z] if (this.Salary == emp.Salary) { return this.Name.CompareTo(emp.Name); } // Default to salary sort. [High to low] return emp.Salary.CompareTo(this.Salary); } public override string ToString() { // String representation. return this.Salary.ToString() +  + this.Name; } } //Calling from Main without implementing IComparable genericClass g1 = new genericClass (); Compilation error : 'Corner.EmployeeWithoutIComparable' cannot be used as type parameter 'T' in the generic type or method 'Corner.genericClass '. There is no implicit reference conversion from 'Corner.EmployeeWithoutIComparable' to 'System.IComparable'. //Calling from Main with struct and implementing IComparable genericClass g1 = new genericClass (); Compilation error : The type 'Corner.EmployeeStruct' must be a reference type in order to use it as parameter 'T' in the generic type or method 'Corner.genericClass ' //Calling from Main with class and implementing IComparable Employee objE = new Employee(); objE.Name = Test1; objE.Salary = 10000; genericClass g1 = new genericClass (); g1.somemethod(objE); This is running fine. Hope it makes clear to you. Thanks