C#
Generics vs object
Learn the type-safety difference between generics and object.
The non-generic alternative: object
In C# object is the base of all types. If you make a property of type object it can hold any value: public object Value { get; set; }. But this approach has a big problem: boxing and required casts.
For example, an int value is boxed when assigned to object; you need an (int) cast to get it back. Casting to the wrong type throws InvalidCastException. Generic classes solve this at the root: Box<int> has no boxing, no casts and errors are caught at compile time.
The hidden cost of boxing
Assigning an int to object is not just syntax; it is a memory event. The value type is boxed on the heap instead of living on the stack. This means extra allocation and copying. Done many times, it slows the program down.
Generic classes avoid boxing: the int inside Box<int> sits directly in the property. This is why List<int> is much faster than the old ArrayList. Generics give type safety and performance at once.
Exercise Compare ObjectBox and Box<T>
Define an ObjectBox class with public object Value { get; set; }. Define a Box<T> generic class with public T Value { get; set; }. In Main create an ObjectBox, set Value = 42, get it back with an (int) cast and print. Do the same with Box<int>; print without a cast.
Show example solution
Write class ObjectBox { public object Value { get; set; } } and class Box<T> { public T Value { get; set; } }. In Main add var ob = new ObjectBox { Value = 42 }; int n = (int)ob.Value; Console.WriteLine(n); var gb = new Box<int> { Value = 42 }; Console.WriteLine(gb.Value);
Example solution:
using System;
class ObjectBox
{
public object Value { get; set; }
}
class Box<T>
{
public T Value { get; set; }
}
class Program
{
static void Main()
{
var ob = new ObjectBox { Value = 42 };
int n = (int)ob.Value;
Console.WriteLine(n);
var gb = new Box<int> { Value = 42 };
Console.WriteLine(gb.Value);
}
}
Test yourself
-
Match each approach to its trait
- object
- Requires boxing
- <T>
- Type safe
- (int) cast
- Runtime risk
- compile error
- Generic guarantee
-
What is needed to get int back from object?
object o = 42;
int n = ______;
- Cast (int)o
- Nothing, n = o
- Boxing operator
- new int(o)
Show answer
Cast (int)o — Correct. (int) cast is needed to unbox from object.
-
The object property
public ____ Value { get; set; } // requires boxing
Show answer
public object Value { get; set; } // requires boxing
Next lesson: Summary - Generics basics
