We've already gone over this defensive code concept in practice earlier when we leveraged the tryParse or the 'is' or 'as' operators, all these constructs are here for us to prevent errors from occurring.
the idea behind defensive code is to prevent exceptions, our goal is to validate our data or what we are trying to do, before an exception is thrown. Hence we are ensuring that code which could though an exception, won't because it will never be executed.
using System;
namespace pc.defensiveCode
{
class Person { }
class Dog { }
class Program
{
static void Main(string[] args)
{
var str = "12g3";
int i;
// We test to see if our 'str' variable is an int
// rather than assume it is
if (int.TryParse(str, out i))
Console.WriteLine($"\"{str}\" is an int");
else
Console.WriteLine($"\"{str}\" is not an int");
object o = DateTime.Now;
// We test to see if our object 'o' is a DateTime
// rather than assume it is
if (o is DateTime)
Console.WriteLine($"{o} is a valid date time");
else
Console.WriteLine("the value of o is not a valid date time");
o = new Person();
if (o is Person && o is Object)
Console.WriteLine("o is a person and object");
else
Console.WriteLine("o is not a person and object");
// We use the as operator to unbox our object
// as a person
var p = o as Person;
// We test to see if our object 'p' is a not null
// rather than assume it is
if (p != null)
Console.WriteLine("p is a person");
else
Console.WriteLine("p is not a person");
// We use the as operator to unbox our object
// as a dog
var d = o as Dog;
// We test to see if our object 'd' is a not null
// rather than assume it is
if (d != null)
Console.WriteLine("d is a dog");
else
Console.WriteLine("d is not a dog");
}
}
}
this is more of a concept than a construct, but defensive code is good code.
