Questions tagged [c#-8.0]
34 questions
0
votes
1
answer
29
Views
expression of type 'T' cannot be handled by a pattern of type '<null>'
Here is a minimal sample:
class C {
public bool F(T x) => x is null;
}
The real code causing the issue is here https://github.com/kofifus/With/blob/master/With.cs#L35
Until today this compiled fine, but I just upgraded to
Microsoft Visual Studio Community 2019 Preview Version 16.1.0 Preview
2.0
The...
1
votes
1
answer
55
Views
Why IAsyncEnumerator doesn't have the Reset method in C#8?
Why IAsyncEnumerator doesn't have the Reset method ? It only has the Current property and the MoveNextAsync() method.
public interface IAsyncEnumerator : IAsyncDisposable
{
T Current
{
get;
}
ValueTask MoveNextAsync();
}
1
votes
1
answer
341
Views
C# 8 positional pattern vs. deconstruction pattern
In the first proposal of pattern matching the recursive pattern was defined with the following grammar:
recursive_pattern
: positional_pattern
| property_pattern
;
Link: https://github.com/dotnet/csharplang/blob/master/proposals/patterns.md
To demonstrate the positional pattern, .Net team has use th...
1
votes
1
answer
37
Views
When C#8 is released, on what frameworks will it run on?
When C# 8 is released, will it be targeting .NET Core 3.x only or will it be able to target existing frameworks too? If so, which ones?
0
votes
0
answer
9
Views
Why IAsyncEnumerator doesn't have the Reset method in C#-8?
Why IAsyncEnumerator doesn't have the Reset method ? It only has the Current property and the MoveNextAsync() method.
public interface IAsyncEnumerator : IAsyncDisposable
{
T Current
{
get;
}
ValueTask MoveNextAsync();
}
1
votes
1
answer
11
Views
What is the default value of Non-Nullable reference types in C# 8?
If I enable nullable reference types , what will be the value of the following string if I declare it like so ?
string text;
6
votes
3
answer
178
Views
What happens with returning IEnumerable if used with async/await (streaming data from SQL Server with Dapper)?
I am using Dapper to stream data from a very large set in SQL Server. It works fine with returning IEnumerable and calling Query(), but when I switch to QueryAsync(), it seems that the program tries to read all of the data from SQL Server instead of streaming.
According to this question, it should w...
4
votes
1
answer
26
Views
Minimal installation of C# 8 command-line compiler for “dotnet build”
We need to install the new C# 8 command-line compiler on our Jenkins server.
We found the 'Build Tools for Visual Studio 2019' package on the Visual Studio Downloads page, but when we select the '.NET Core build tools' workload, it wants to install almost 2GB of stuff. This is a problem, as our Jenk...
1
votes
0
answer
5
Views
Multiple cases in c# 8.0 switch
In traditional c# switch we have such construction,where we can aggregate multiple cases. How can it be done in new c# 8.0 switch construction ?
switch (value)
{
case 1:
case 2:
case 3:
//do some stuff
break;
case 4:
case 5:
case 6:
//do some different stuff
break;
default:
//default stuff
break;
}
1
votes
2
answer
0
Views
How to mark a NonNullable reference property as safe? [duplicate]
This question already has an answer here:
Non-nullable string type, how to use with Asp.Net Core options
1 answer
I have an entity which I use in my EntityFramework model.
public class Entity
{
public int Id { get; set; }
public string Value { get; set; }
}
After enabling nullable reference types c...
4
votes
3
answer
95
Views
What is Range and Index types in c# 8?
In c# 8 add two new types to System namespace as
System.Index
and
System.Range
How work this classes and When can use them?
1
votes
1
answer
43
Views
How to mark a default return value in C# 8 as nullable for classes only?
I'm currently trying to apply the new C# 8.0 non-nullable reference type feature to existing code, and don't know how to fix the CS8603 warning in the following data deserialization method:
T ReadOptional() where T : IEntity, new()
{
if (ReadBoolean())
{
T instance = new T();
instance.Read(this); //...
1
votes
1
answer
60
Views
Can I define C# 8 beta compatible indexers in C# 7?
It seems, that they require System.Index and System.Range
I can't find any NuGet packages that would provide these, similar to ValueTuple
1
votes
2
answer
103
Views
What is the difference between NullableContextOptions and NullableReferenceTypes?
I've been playing with new c# 8.0 NullableReferenceTypes feature for a while.
And I'm little bit confused about turning this feature on via changing .csproj file.
I mean in order to enable this feature you have to put the following lines in your .csproj file:
8.0
enable
But also I've found another o...
0
votes
0
answer
33
Views
The best practice when using c# 8.0 null reference type during deserialization
I am trying the c# 8.0 and want to enable the null reference type check for the whole project. And I hope I could improve my code design, but not to disable this check in some code scope.
I met a problem when I deserialize an object graph. The object have reference with each other, but for the final...
6
votes
3
answer
233
Views
Relationship between C# 8.0, NET Core 3.0 and Visual Studio
The article Building C# 8.0 states
The current plan is that C# 8.0 will ship at the same time as .NET Core 3.0. However, the features will start to come alive with the previews of Visual Studio 2019 that we are working on.
What is the relationship between C# 8.0, NET Core 3.0 and Visual Studio?
As a...
1
votes
0
answer
45
Views
By which criteria range is applied to arrays and strings in C#8?
I'm looking through C#8 ranges and cannot understand how exactly the application of the Range is restricted to arrays and strings only.
I have thought that it is somehow related to interface array implements. It implements ICloneable, IList, ICollection, IEnumerable, IStructuralComparable, IStructur...
42
votes
2
answer
1.4k
Views
What does null! statement mean?
I've recently seen the following code:
public class Person
{
//line 1
public string FirstName { get; }
//line 2
public string LastName { get; } = null!;
//assign null is possible
public string? MiddleName {get; } = null;
public Person(string firstName, string lastName, string middleName)
{
FirstName...
1
votes
1
answer
0
Views
C# 8.0 availability in Visual Studio 2017?
I'd like to use C# 8.0 (especially ranges and non-nullable reference types). I only found some information that there is a preview of it in the new VS2019 (even that is 2 months old now).
Are there any plans that C# 8.0 is eventually also coming to VS17?
0
votes
0
answer
21
Views
Does default implementation of Interface members in C# 8 relates to overcome multiple inheritance problem of abstract class?
I'm reading this blog of .NET Engineering Team and they have introduced a
new feature of default implementation for Interface. I'm confused related to its motive other than multiple level inheritance problem of abstract class. Other than that I'm not able to figure out any other benefit. Consdier th...
5
votes
2
answer
145
Views
IAsyncEnumerable<> broken in VS 2019 preview 2 (Core 3.0 preview 1)
After installing VS 2019 preview 2 i get a great number of errors. Error demo code:
public class Class1 {
public static async IAsyncEnumerable Get()
{
for( int i = 0; i < 10; i++ ) {
await Task.Delay( 100 );
yield return i;
}
}
}
and nothig more (a new dll project)!
With preview 1 was ok.
The proj...
131
votes
1
answer
5.8k
Views
Why doesn't the new hat-operator index from the C# 8 array-slicing feature start at 0?
C# 8.0 introduces a convenient way to slice arrays - see official C# 8.0 blogpost.
The syntax to access the last element of an array is
int value[] = { 10, 11, 12, 13 };
int a = value[^1]; // 13
int b = value[^2]; // 12
I'm wondering why the indexing for accessing the elements backwards starts at...
0
votes
2
answer
91
Views
Default interface methods and default values for Auto Properties
Given that an auto property compiles to a get_method, a set_method and a private variable and since C# 8 is introducing default interface methods
Can properties in Interfaces have default implementations?
Especially a get only property?
1
votes
1
answer
109
Views
How to enable Nullable Reference Types feature of C# 8.0 for the whole project
According to the anouncement of the new C# 8.0 feature named 'nullable reference types' it can be enabled for the whole project.
(mentioned here: https://youtu.be/VdC0aoa7ung?t=137)
But how to enable it for the project? Did not find any new appropriate option in Project Properties window in Visual S...
3
votes
3
answer
160
Views
C# 8 - multiple inheritance “abstract class”? [duplicate]
This question already has an answer here:
Default Interface Implementations. What is deep meaningful difference now, between abstract class and interface?
3 answers
It seems to me like the C# 8.0 feature, default interface member implementation, essentially allows one to create implementations at t...
1
votes
3
answer
123
Views
Does C# 8 annotate nullable properties and parameters?
I'm curious about how nullable reference types work, not in your own codebase, but with an already compiled library. Will C# be able to know if a property or parameter is nullable, perhaps checking the existance of some compiler-added attribute?
3
votes
1
answer
133
Views
Can new C# language features be used to to clean-up Task.WhenAll syntax?
With 'async everywhere', the ability to fire off multiple heterogeneous operations is becoming more frequent. The current Task.WhenAll method returns its results as an array and requires all tasks to return the same kind of object which makes its usage a bit clumsy. I'd like to be able to write......
3
votes
2
answer
1.2k
Views
If default interface methods are implemented in C# 8.0 why would I ever need abstract classes? [closed]
I recently ran into a list of features that are being considered for addition in the next version of C#. One of them is called 'default interface methods':
https://github.com/dotnet/csharplang/blob/master/proposals/default-interface-methods.md
In short, it will allow you to define actual method impl...
42
votes
8
answer
17.5k
Views
How would you implement a “trait” design-pattern in C#?
I know the feature doesn't exist in C#, but PHP recently added a feature called Traits which I thought was a bit silly at first until I started thinking about it.
Say I have a base class called Client. Client has a single property called Name.
Now I'm developing a re-usable application that will be...
4
votes
1
answer
750
Views
Nullable Reference Types with C# 8
Null reference exceptions are one of the top sources of program failures. Tony Hoare called it his billion dollar mistake. So I'm particularly looking forward to C# 8 and the new nullable reference types feature. I think I've got a pretty good grasp of the feature and what it's going to mean for my...
8
votes
2
answer
372
Views
Default Interface Methods in C# 8
Consider the following code example:
public interface IPlayer
{
int Attack(int amount);
}
public interface IPowerPlayer: IPlayer
{
int IPlayer.Attack(int amount)
{
return amount + 50;
}
}
public interface ILimitedPlayer: IPlayer
{
new int Attack(int amount)
{
return amount + 10;
}
}
public class Pla...
7
votes
3
answer
433
Views
Default Interface Implementations. What is deep meaningful difference now, between abstract class and interface?
I know that an abstract class is a special kind of class that cannot be instantiated. An abstract class is only to be sub-classed (inherited from). In other words, it only allows other classes to inherit from it but cannot be instantiated. The advantage is that it enforces certain hierarchies for al...
4
votes
3
answer
97
Views
C# 8 - multiple inheritance “abstract class”?
It seems to me like the C# 8.0 feature, default interface member implementation, essentially allows one to create implementations at the interface level. Pairing that with the fact that a class can implement multiple interfaces, it seems eerily close to a multiple inheritance structure for classes....
4
votes
2
answer
102
Views
Determine if type reference is nullable/non-nullable
Using the upcoming C# 8 nullable reference type feature, how can I tell if the type signature for a field/method/ property etc is a nullable or non-nullable reference type at runtime?