[andygocke]

> MS have done is to outsource the issue to all C# devs

Let's be clear: breaking dozens of tools because of a change to the IL format also outsources an issue to all C# devs. The .NET IL format has been basically unchanged since .NET 2.0 and huge numbers of people take very hard dependencies on the exact things they do and do not expect. I don't expect we would have been able to make significant changes due to the breaking change impact.

> A possible approach I mentioned

This would likely be even harder to understand. For better or worse, the .NET design is that external initializers happen _after_ the constructor runs. That's been true all the way back to when the initializer syntax was first introduced in C# 3. Making regular initializers and `with` initializers have inverted order strikes me as being way worse.

If I could go back in time, I think the main change to C# I would make would be to enforce that the constructor always runs after all external initialization.

[louthy]

Slightly confused. My suggestion was to run the initialisers after the new object has been constructed (cloned+modified). The semantics are the same as you describe even if the underlying implementation is different.

What am I missing?

[andygocke]

There are two types of initializers: internal and external. Internal are inside the type, like field and property initializers. External are outside, like object initializers, collection initializers, and ‘with’ clauses.

Internal initializers are run as part of the constructor, before any user code. External initializers are run after the constructor, on the constructed object.

For instance:

  class C
  {
    public int P = 5;
  }

  var c = new C { P = 3 };

`c.P` has the value 3.

In your example:

    var n2 = n1.<Clone>$();
    n2.Value = 3;                    // 'with' field setters
    n2.<OnPostCloneInitialise>();  // run the initialisers

The “PostCloneInitializers” you’re running are the field initializers, so the order is backwards. You’re overwriting the value of the external initializers with the internal initializers.