I suggest we ...

Copy-and-update on class types and on records of different types.

People sometimes find it hard to transition from records to class types - something which comes up when seeking to encapsulate some of the details of the record type.

One particular reason for this is because their codebase may uses copy-and-update on record types. One approach to easing the transition would be to support copy-and-update on class types, as long as the class type follows a particular design pattern.

One pattern-based approach could permit both normal record syntax and copy-and-update syntax, e.g.

type R(a:int, b:int) =
member x.A = a
member x.B = b
member x.C = f(a,b)

{ a = e1; b = e2 } --> R(a=e1,b=e2}
{ r with a = e1} --> R(a=e1,b=r.B)

Whether there were one or two attributes (one for 'RecordSyntax' and one for 'CopyAndUpdateSyntax') would be up for discussion. Presumably using either attribute would give result in a declaration-time check that members exist to match constructor arguments.

Matching uppercase properties to lowercase argument names is somewhat inelegant but in the balance is likely to be a reasonable price to pay for following .NET and F# design norms.

25 votes
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