Allow parameterless constructors in record structs

[jcouv]

[This issue is referenced in source]

When the "record structs" feature gets merged with the "parameterless struct constructor" feature, we may need to make some adjustments to record structs.

Some scenarios are interesting:

record struct S1(); // is this allowed?

_ = new S2(); // what is executed?
record struct S2(int I)
{
   int Field = M(I);
   static int M(int i) => i;
}

record struct S3
{
  int Field = 3; // is this allowed?
}

record struct S4()
{
  int Field = 3; // is this allowed?
}

[SteveDunn]

Hi - is this in .NET 6 preview 6? It'd be great if a user could specify a validation method so that the struct could never be created with an invalid value, e.g.

public record struct Age(int Value)
{
   public Age()
  {
    if(Value < 0) throw new InvalidOperationException("Ages cannot be negative");
  } 
}

[jcouv]

No, it barely missed .NET 6 preview 7. It'll be in the following preview.

[SteveDunn]

I'm ideally looking for the succinctness of records, the memory traits of value-type primitives, and constraits that mean no invalid instances can be created. https://dunnhq.com/posts/2021/primitive-obsession/

[jcouv]

Update: it did make it into .NET 6 preview 7 after all (and VS 2022 preview 3).