What Are New Features in c# 8.0?
Indices and
ranges -
C# 8.0 adds the following features and
enhancements to the C# language:
=>Read-only members
=>Default interface methods
=>Pattern matching enhancements:
i) Witch expressions
j) Property patterns
k) Tuple patterns
l) Positional patterns
=>Using declarations
=>Static local functions
=>Disposable ref structs
=>Nullable reference types
=>Asynchronous streams
=>Indices and ranges
=>Null-coalescing assignment
=>Unmanaged constructed types
=>Stackalloc in nested expressions
=>Enhancement of interpolated verbatim strings
You can see n-depth articles with examples –
Readonly Member -
Provide a way to specify individual instance
members on a struct do not modify state, in the same way that read-only struct
specifies no instance members modify state.
Allows you to apply the read-only
modifier to any member of a struct.
public struct YValue
{
private int Y { get; set; }
public readonly int
IncreaseY()
{
// This will
not compile: C# 8
Y = Y + 1;
var newY = Y + 1; // OK
return newY;
}
}
Default Interface
Methods -
Allows you to add new functionality to your
interfaces of your libraries and ensure the backward compatibility with code
written for older versions of those interfaces.
interface IWriteLine
{
public void
WriteLine()
{
Console.WriteLine("Wow C# 8!");
}
}
Pattern Matching
Enhancements -
Provides the ability to deconstruct matched
objects, and giving you access to parts of their data structures.
C# offers
a rich set of patterns that can be used for matching:
1.
Switch expressions
2.
Property patterns
3.
Tuple patterns
4.
Positional patterns
There
are several syntax improvements here:
1. The
variable comes before the switch keyword. The different order makes it visually
easy to distinguish the switch expression from the switch statement.
2. The
case and : elements are replaced
with =>. It's more concise and
intuitive.
3. The
default case is replaced with a _
discard.
4. The
bodies are expressions, not statements.
static bool
Positive(Point p) => p switch
{
(0, 0) => true,
(var x, var y) when x > 0 && y > 0 => true,
_ => false
};
Nullable
Reference Types -
Emits a compiler warning or error if a variable
that must not be null is assigned to null.
string? nullableString = null;
//
WARNING: may be null! Take care!
Console.WriteLine(nullableString.Length)
The
goal of this feature is to:
Allow developers to express
whether a variable, parameter or result of a reference type is intended to be
null or not.
Provide warnings when such
variables, parameters and results are not used according to that intent.
Using Declarations
-
The language will add two new capabilities around
the using statement in order to make resource management simpler: using should
recognize a disposable pattern in addition to IDisposable and add a using
declaration to the language.
Enhances the ‘using’ operator to use with
Patterns and make it more natural.
using var repository = new Repository();
Console.WriteLine(repository.First());
// repository is disposed
here!
Enhancement of interpolated verbatim
strings –
Order of the $ and @ tokens in interpolated
verbatim strings can be any: both $@"..." and @$"..." are
valid interpolated verbatim strings. In earlier C# versions, the $ token must
appear before the @ token.
Allows @$““as a verbatim
interpolated string,
var file = @$"c:\temp\{filename}";
Asynchronous Streams
-
Starting with C# 8.0, you can create and consume
streams asynchronously. A method that returns an asynchronous stream has three
properties:
1) It's declared with the async modifier.
2) It returns an IAsyncEnumerable<T>.
3) The method contains yield return statements to
return successive elements in the asynchronous stream.
Allows having enumerators that support async
operations.
await foreach (var x in enumerable)
{
Console.WriteLine(x);
}
Null-coalescing
Assignment -
C# 8.0 introduces the null-coalescing assignment
operator ??=. You can use the ??= operator to assign the value of its
right-hand operand to its left-hand operand only if the left-hand operand
evaluates to null.
Simplifies a common coding pattern where a
variable is assigned a value if it is null. It is common to see the code of the
form:
//In C# 1
to 7
if (variable == null)
{
variable = expression;
}
// In C#
8
variable
??= expression;
Static
local functions –
You can now add the static modifier to local
functions to ensure that local function doesn't capture (reference) any
variables from the enclosing scope. Allows you to add the 'static' modifier to
the local functions.
int AddFiveAndSeven()
{
int y = 1; int x = 2;
return Add(x, y);
static int Add(int o, int t) => o + t;
}
Unmanaged Constructed
Types -
Allows you to take a pointer to unmanaged
constructed types, such as ValueTuple<int, int>, as long as all the elements
of the generic type are unmanaged.
struct Foo<T> where T : unmanaged
{
}
public unsafe void Test()
{
var foo = new Foo<int>();
var bar = &foo; // C# 8
}
Stackalloc in
Nested Expressions –
The result of a stackalloc expression is of the System.Span<T> or System.ReadOnlySpan<T> type.
Span<int> set = stackalloc[] { 1, 2, 3, 4, 5, 6};
var
subSet = set.Slice(3, 2);
foreach (var n in subSet){
Console.WriteLine(n); // Output:
4 5
}
Disposable ref
structs -
A struct declared with the ref modifier may not
implement any interfaces and so can't implement IDisposable. Therefore, to
enable a ref struct to be disposed, it must have an accessible void Dispose()
method. This feature also applies to read-only ref struct declarations.
Allows you to use the ‘using’ pattern with ref
struct or readonly ref struct‘.
//
Pattern-based using for ref struct
ref struct Test
{
public void
Dispose() { }
}
using var test = new Test();
// test is disposed here!
Indices and ranges provide a succinct syntax for
accessing single elements or ranges in a sequence.
1) This language support relies on two new types,
and two new operators:
2) System.Index represents an index into a
sequence.
3) The index from end operator ^, which specifies
that an index is relative to the end of the sequence.
4) System.Range represents a sub range of a
sequence.
5) The range operator .., which specifies the
start and end of a range as its operands.
Allows you to use more natural syntax for
specifying subranges in an array or a collection.
int[] a = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
Index:
Used to obtain the collection from the beginning or from the end.
// Number 4
from end of the collection
Index i2
= ^4;
Console.WriteLine($"{a[i2]}");
// "6"
//Range:
Access a sub-collection(slice) from a collection.
var slice = a[i1..i2]; // { 3, 4, 5 }
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