1) Default Interface Methods
interface IWriteLine
{
public void WriteLine()
{
Console.WriteLine("Wow C# 8!");
}
}
2) Nullable reference type
string? nullableString = null;
Console.WriteLine(nullableString.Length);
3) Advanced Pattern Matching
Example
var point = new 3DPoint(1, 2, 3); //x=1, y=2, z=3
if (point is 3DPoint(1, var myY, _))
{
// Code here will be executed only if the point .X == 1, myY is a new variable
// that can be used in this scope.
}
4) Async streams
await foreach (var x in enumerable)
{
Console.WriteLine(x);
}
5) Ranges
Index i1 = 3; // number 3 from beginning
Index i2 = ^4; // number 4 from end
int[] a = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
Console.WriteLine($"{a[i1]}, {a[i2]}"); // "3, 6"
6) Caller Expression Attribute
public static class Verify {
public static void InRange(int argument, int low, int high,
[CallerArgumentExpression("argument")] string argumentExpression = null,
[CallerArgumentExpression("low")] string lowExpression = null,
[CallerArgumentExpression("high")] string highExpression = null) {
if (argument < low) {
throw new ArgumentOutOfRangeException(paramName: argumentExpression, message: $ " {argumentExpression} ({argument}) cannot be less than {lowExpression} ({low}).");
}
if (argument > high) {
throw new ArgumentOutOfRangeException(paramName: argumentExpression, message: $ "{argumentExpression} ({argument}) cannot be greater than {highExpression} ({high}).");
}
}
public static void NotNull < T > (T argument,
[CallerArgumentExpression("argument")] string argumentExpression = null)
where T: class {
if (argument == null) throw new ArgumentNullException(paramName: argumentExpression);
}
}
// CallerArgumentExpression: convert the expressions to a string!
Verify.NotNull(array); // paramName: "array"
// paramName: "index"
// Error message by wrong Index:
"index (-1) cannot be less than 0 (0).", or
// "index (6) cannot be greater than array.Length - 1 (5)."
Verify.InRange(index, 0, array.Length - 1);
7) Default in deconstruction
(int x, string y) = (default, default); // C# 7
(int x, string y) = default; // C# 8
8) Using declarations
// C# Oldy Style
using (var repository = new Repository())
{
} // repository is disposed here!
// vs.C# 8
using var repository = new Repository();
Console.WriteLine(repository.First());
// repository is disposed here!
9) Generic attributes
public class GenericAttribute<T> : Attribute { }
public class ValidatesAttribute<T> : Attribute {}
[Validates<string>]
public class StringValidation {}
[Validates<int>]
public class IntegerValidation{}
10) Static Local Functions
int AddFiveAndSeven()
{
int y = 5; int x = 7;
return Add(x, y);
static int Add(int left, int right) => left + right;
}
interface IWriteLine
{
public void WriteLine()
{
Console.WriteLine("Wow C# 8!");
}
}
2) Nullable reference type
string? nullableString = null;
Console.WriteLine(nullableString.Length);
3) Advanced Pattern Matching
Example
var point = new 3DPoint(1, 2, 3); //x=1, y=2, z=3
if (point is 3DPoint(1, var myY, _))
{
// Code here will be executed only if the point .X == 1, myY is a new variable
// that can be used in this scope.
}
4) Async streams
await foreach (var x in enumerable)
{
Console.WriteLine(x);
}
5) Ranges
Index i1 = 3; // number 3 from beginning
Index i2 = ^4; // number 4 from end
int[] a = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
Console.WriteLine($"{a[i1]}, {a[i2]}"); // "3, 6"
6) Caller Expression Attribute
public static class Verify {
public static void InRange(int argument, int low, int high,
[CallerArgumentExpression("argument")] string argumentExpression = null,
[CallerArgumentExpression("low")] string lowExpression = null,
[CallerArgumentExpression("high")] string highExpression = null) {
if (argument < low) {
throw new ArgumentOutOfRangeException(paramName: argumentExpression, message: $ " {argumentExpression} ({argument}) cannot be less than {lowExpression} ({low}).");
}
if (argument > high) {
throw new ArgumentOutOfRangeException(paramName: argumentExpression, message: $ "{argumentExpression} ({argument}) cannot be greater than {highExpression} ({high}).");
}
}
public static void NotNull < T > (T argument,
[CallerArgumentExpression("argument")] string argumentExpression = null)
where T: class {
if (argument == null) throw new ArgumentNullException(paramName: argumentExpression);
}
}
// CallerArgumentExpression: convert the expressions to a string!
Verify.NotNull(array); // paramName: "array"
// paramName: "index"
// Error message by wrong Index:
"index (-1) cannot be less than 0 (0).", or
// "index (6) cannot be greater than array.Length - 1 (5)."
Verify.InRange(index, 0, array.Length - 1);
7) Default in deconstruction
(int x, string y) = (default, default); // C# 7
(int x, string y) = default; // C# 8
8) Using declarations
// C# Oldy Style
using (var repository = new Repository())
{
} // repository is disposed here!
// vs.C# 8
using var repository = new Repository();
Console.WriteLine(repository.First());
// repository is disposed here!
9) Generic attributes
public class GenericAttribute<T> : Attribute { }
public class ValidatesAttribute<T> : Attribute {}
[Validates<string>]
public class StringValidation {}
[Validates<int>]
public class IntegerValidation{}
10) Static Local Functions
int AddFiveAndSeven()
{
int y = 5; int x = 7;
return Add(x, y);
static int Add(int left, int right) => left + right;
}
