[Proposal]: Equivalent to "throws" keyword

[vbakc]

Equivalent to throws keyword

• Proposed
• Prototype: Not Started
• Implementation: Not Started
• Specification: Not Started

Summary

In C# you do not really know whether can method throw exception or not. All you can do now is use method naming conventions (btw, I did not found any) like in dynamic languages such as Ruby. Which is a shame for such beautiful, static language as C#. What I suggest is to adopt Java's throw keyword equivalent.

Motivation

This will help to reduce errors in runtime.

Detailed design

In Java if method can throw exception you must either catch it or specify, that this method can throw exception of some type, even if you do not use this method at all.

class Main {
  public static void test() throws Exception {
    if (false) {
      throw new Exception();
    }
  }

  public static void main(String[] args) { }
}

It can be optional or mandatory.

Suggested C# syntax:

class Program
{
  static void test() ! Exception
  {
    throw new Exception();
  }
        
  static void Main(string[] args)
  {
    Console.WriteLine("Hello World!");
  }
}

Drawbacks

Alternatives

Unresolved questions

Design meetings

[YairHalberstadt]

C# very intentionally did not adopt java's checked exceptions, which are also widely hated by Java developers - both scala and kotlin don't have them despite being made for the JVM for example.

I think you'll have to explain why that decision should be revisited, or come up with a design that avoids many of the pitfalls of Java's design for this to be considered.

A much more promising direction is to take a leaf out of functional languages, and introduce a Result<T, TError> type along with coroutines for working with it. The advantage of this approach is that it composes much better since it's just an ordinary type system construct.

[YairHalberstadt]

See here for why C# doesn't have checked exceptions https://www.artima.com/intv/handcuffs.html

[dstarkowski]

There's an <exception/> tag in xml docs. Maybe better solution would be to surface it in IDE? Of course the usual "you could write an analyzer" answer also applies.