If you find any mistakes in the fifth edition, C# 9 and .NET 5, or if you have suggestions for improvements, then please raise an issue in this repository or email me at markjprice (at) gmail.com.
Hi! This isn't an errata.
I know that I've submitted a few potential errata, but I just wanted to say that this is one of the most cleanly written programming books I've read in quite a while. The author clearly cares about the quality of his book and takes time to anticipate what a reader might run into. It is a pleasure working through it. Keep up the great work!
I hope you share this comment with the author to let him know that his work is greatly enjoyed and appreciated.
In the book, I say that the double type has some special static members, including one named Infinity. This is wrong. There are two members named PositiveInfinity and NegativeInfinity.
The book says, "Visual Studio has a feature called workspaces that enables this." It should have said, "Visual Studio Code has a feature called workspaces that enables this."
In the code example, I show assigning a string value to a dynamically-typed variable, as shown in the following code:
// storing a string in a dynamic object
dynamic anotherName = "Ahmed";
// this compiles but would throw an exception at run-time
// if you later store a data type that does not have a
// property named Length
int length = anotherName.Length;
The above example code does not throw an exception because at the time we get the Length property, the value stored in anotherName is a string which does have a Length property.
The example would have been clearer if I had shown some examples of assigning values with other data types that do and do not have a Length property, as shown in the following code:
// storing a string in a dynamic object
// string has a Length property
dynamic anotherName = "Ahmed";
// int does not have a Length property
anotherName = 12;
// an array of any type has a Length property
// anotherName = new[] { 3, 5, 7 };
// this compiles but would throw an exception at run-time
// if you had stored a value with a data type that does not
// have a property named Length
int length = anotherName.Length;
The above example code does throw an exception because at the time we get the Length property, the value stored in anotherName is an int which does not have a Length property, as shown in the following output:
Unhandled exception. Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'int' does not contain a definition for 'Length'
at CallSite.Target(Closure , CallSite , Object )
at System.Dynamic.UpdateDelegates.UpdateAndExecute1[T0,TRet](CallSite site, T0 arg0)
at Variables.Program.Main(String[] args) in /Users/markjprice/Code/Chapter02/Variables/Program.cs:line 34
If you uncomment the statement that assigns an array of int values, then the code works without throwing an exception because all arrays have a Length property.
In Step 1, the code uses ToInt as a label for the output. It should use ToInt32 to match the actual method name. The following code:
double[] doubles = new[]
{ 9.49, 9.5, 9.51, 10.49, 10.5, 10.51 };
foreach (double n in doubles)
{
WriteLine($"ToInt({n}) is {ToInt32(n)}");
}
Should be:
double[] doubles = new[]
{ 9.49, 9.5, 9.51, 10.49, 10.5, 10.51 };
foreach (double n in doubles)
{
WriteLine($"ToInt32({n}) is {ToInt32(n)}");
}
The output shown in Step 2 would then look like the following:
ToInt32(9.49) is 9
ToInt32(9.5) is 10
ToInt32(9.51) is 10
ToInt32(10.49) is 10
ToInt32(10.5) is 10
ToInt32(10.51) is 11
The switch case value of ME is commented as Maryland. ME is the abbreviation for Maine.
The code example is about deconstructing tuples into individual parts. It shows that you do not have to return a named tuple because during deconstruction the syntax allows explicit naming of the individual parts, as shown in the following code:
public (string, int) GetFruit()
{
return ("Apples", 5);
}
public (string Name, int Number) GetNamedFruit()
{
return (Name: "Apples", Number: 5);
}
(string fruitName, int fruitNumber) = bob.GetFruit() // GetNamedFruit would also work but is not necessary
WriteLine($"Deconstructed: {fruitName}, {fruitNumber}");
In Step 5, the book says to "Comment out the attempt to set the LastName property after instantiation." This should have said, "Comment out the attempt to set the FirstName property after instantiation."
In Step 1, the code in the book to define a positional record uses the original keywords, data class, that were used in early previews of .NET 5, as shown in the following code:
// simpler way to define a record that does the equivalent
public data class ImmutableAnimal(string Name, string Species);
It should have been updated to use the keyword, record, that was used in later previews and the final release of .NET 5, as shown in the following code:
// simpler way to define a record that does the equivalent
public record ImmutableAnimal(string Name, string Species);
The code in the GitHub repository was already correct. It is only the print book that has this errata.
Step 3 says to "add a colon and enter IComparable<Person>". This works if you started a new project in Chapter 6. But if you continued with your project from Chapter 5 then the Person class already has a colon and inherits from System.Object. So the instruction in that case should be, "add a comma and enter IComparable<Person>", as shown in the following code:
public class Person : System.Object, IComparable<Person>
The code in the book uses 2000 iterations for PBKDF2 to generate a key and initialization vector (IV) for the encryption algorithm. I said that this is "double the recommended salt size and iteration count". I first wrote that code and statement in the fall of 2015 for the first edition and I have neglected to keep it updated. More than five years later, 2000 is not enough! I have updated the project in GitHub to use 50,000 iterations, as shown in the following code:
// iterations should be high enough to take at least 100ms to
// generate a Key and IV on the target machine. 50,000 iterations
// takes 131ms on my 3.3 GHz Dual-Core Intel Core i7 MacBook Pro.
private static readonly int iterations = 50_000;
To avoid updating the value every edition, what I will say in the sixth edition is that the best iteration count for PBKDF2 is whatever number takes about 100ms on the target machine. Now that anyone can buy a $699 Apple Mac mini with amazing performance, that recommendation could be closer to a million iterations! And that value will only increase as time passes.
As I said on page 334, "If security is important to you (and it should be!), then hire an experienced security expert for guidance rather than relying on advice found online." Or in a generalist programming book.
To make it easier to complete Exercise 10.3, I split the CheckPassword method into two overloaded methods, as shown in the following code:
// check a user's password that is stored
// in the private static dictionary Users
public static bool CheckPassword(string username, string password)
{
if (!Users.ContainsKey(username))
{
return false;
}
var user = Users[username];
return CheckPassword(username, password,
user.Salt, user.SaltedHashedPassword);
}
// check a user's password using salt and hashed password
public static bool CheckPassword(string username, string password,
string salt, string hashedPassword)
{
// re-generate the salted and hashed password
var saltedhashedPassword = SaltAndHashPassword(
password, salt);
return (saltedhashedPassword == hashedPassword);
}
In Step 3, when downloading SQLite for Windows, make sure to download the tools ZIP not the dll ZIPs, as shown in the following screenshot:
- What interface must an object implement to be enumerated over by using the
foreachstatement?
Answer: An object must implement the IEnumerable interface.
Although an object does not have to formally implement an interface to be enumerable using foreach, the question asks "What interface...", so the answer must be the name of an interface. IEnumerable is that interface. In the next edition, I will put quote-marks around "implement" so it is clear that it can either formally implement the IEnumerable interface or just have matching members.
- In Visual Studio Code, what is the difference between pressing F5; Ctrl or Cmd + F5; Shift + F5; and Ctrl or Cmd + Shift + F5?
"Ctrl or Cmd + F5 saves, compiles, and runs the application with the debugger attached" should be "Ctrl or Cmd + F5 saves, compiles, and runs the application without the debugger attached"