C# – TooSlowException

Tag: C#

The 8 most missing features in C#

March 1, 2021 by Konrad Kokosa·9 Comments

Sometimes you may hear oppinions that there are too many changes introduced to the C# and/or too fast. That people get lost and confused about all this new syntax and feature added here and there. And while one may argue or not, I would like to look at this topic from a different angle – what are you missing in C#? What single functionality would you enjoy the most?

I’ve asked the same question here and there (in Polish) and here are aggregated results, sorted by popularity, with some additional remarks from my side:

1. Discriminated unions

The clear winner is a possibility to use “discriminated unions”. There is an ongoing proposal about them already. The most often mentioned wishes here are to have good pattern matching support (we hope so!) and F# DU compatiliby (unlikely, like in the case with records).Continue reading

6 less popular facts about C# 9 records

November 19, 2020 by Konrad Kokosa·5 Comments

A lot of C# 9-related content is around. Very often, records are mentioned as one of the most interestning new features. So, while we can find A LOT of buzz around them, I wanted to provide a distilled set of facts typically not presented when describing them.

Fact #1. You can use them in pre-.NET 5

Records has been announced as C# 9 feature (and thus .NET 5), and it is the officially supported way. But you can “not officialy” use most C# 9 features in earlier frameworks, as they don’t need the new runtime support. So, if being not “officially supported” does not bother you too much, just set proper LangVersion in csproj and you are (almost) done:

<PropertyGroup>
   <TargetFramework>netcoreapp3.1</TargetFramework>
   <LangVersion>9</LangVersion>
</PropertyGroup>

<TargetFramework>netcoreapp3.1</TargetFramework>

</PropertyGroup>

Trying to compile super typical example like the following:

public record Person
{
   public string FirstName { get; init; }
   public string LastName { get; init; }
}

public record Person

{

public string FirstName { get; init; }

public string LastName { get; init; }

}

will still not compile, complaining about the lack of mysterious IsExternalInit type:

Error CS0518 Predefined type 'System.Runtime.CompilerServices.IsExternalInit' is not defined or imported

1	Error CS0518 Predefined type 'System.Runtime.CompilerServices.IsExternalInit' is not defined or imported

To be funny, the workaround is just to define it in your project (exactly as it is in the newer CoreLib, shipped with .NET 5):

namespace System.Runtime.CompilerServices
{
   public class IsExternalInit{}
}

namespace System.Runtime.CompilerServices

{

public class IsExternalInit{}

}

BTW, IsExternalInit is not required for the record usage by itself, but for init as discussed in https://github.com/dotnet/runtime/issues/34978 and https://github.com/dotnet/runtime/pull/37763. So if creating mutable records is ok, no need for that.

Sidenote: If you are interested what more you can “not officially” use, look at Using C# 9 outside .NET 5 #47701 discussion.Continue reading