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C# 6 Cuts

In a recent thread on CodePlex Mads Torgeson, C# Language PM at Microsoft, announced 2 of the key features planned for C# 6 release have now been cut:

  • Primary constructors
  • Declaration expressions

According to Mads:

They are both characterized by having large amounts of downstream work still remaining.

primary constructors could grow up to become a full-blown record feature

Reading between the lines Mads seems to be saying the features weren’t finished and even if they were they seemed to conflict with a potential record feature currently being prototyped.

The full thread is here: Changes to the language feature set

Language Design

I think there’s two distinct options when adding new features to an existing language with a large user base:

  • upfront design
  • implement incrementally

Upfront design should mean that all cases are met but comes at a time-to-market cost, where as an incremental implementation means quick releases with the potential risk of either sub-optimal syntax or backward compatibility issues when applying more features.

It appeared at the high level that the C# team’s had initially opted for the incremental option. The feature cuts however suggest to me that there may have been a change in direction towards more upfront design.

Primary Constructors

The primary constructors feature was intended to reduce the verbosity of C#’s class declaration syntax. The new feature appeared to be inspired by F# ’s class syntax.

If you like the idea of a lighter syntax for class declarations then you may just want to try F# which already has a well thought out mature implementation, i.e.

type Person(name:string, age:int) =
    member this.Name = name
    member this.Age = age

Or for simple types use the even simpler record type:

type Person = { Name:string, Age:int }

Note: on top of lighter class syntax F# also packs a whole raft of cool features not available in C#, including powerful pattern matching and data access via Type Providers.

Declaration Expressions

Declaration expressions was again designed to reduce verbosity in C# providing a lighter syntax for handling out parameters. Out parameters are used in C# to allow a method to return multiple values:

int result;
bool success = Int32.TryParse("123", out result);

Again handling multiple return values is handled elegantly in F# which employs first-class tuples, i.e.

let success, value = Int32.TryParse("123")

As shown above, C# out parameters can be simply captured in F# as if the method were returning multiple values as a tuple.


The first time I saw Mads publicly announce the now cut primary constructor syntax and declaration expressions was nearly a year ago at NDC London. At the time the features were announced with a number of disclaimers that they may not actually ship. I think in future it may be better for everyone to take those disclaimers with more than just a pinch of salt.

Comments (2) -

  • Lee Stutzman

    10/3/2014 6:08:07 AM |

    Very unfortunate, I didn't care too much for primary constructors but declaration expressions would have been very nice.

  • Dan Sutton

    10/3/2014 9:47:21 AM |

    Can't say I'm too upset about it; I understand what they were trying to do, but the proposed implementation was just a little too write-only for my liking.

    I think at this stage there are so many languages around that legibility and common knowledge trump arcane knowledge of how to save a few bytes in the source code... when that doesn't change anything in the compiled program.

    Had they come up with something which would've improved the nature of the compiled product, I'd have a different opinion, but the proposed implementation was of syntactic sugar only. Raw sugar. Unprocessed. Dark... and bitter...

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