Improved "with keyword" with nested assignment / referential paths

[dellamonica]

Make the with keyword more powerful by allowing it to operate on nested properties.
For instance, let A be a record type containing another record Type B under property PropB.

instanceOfA = instanceOfA with { PropB.AnotherProp = "changed" } 

This would be lowered to

instanceOfA = instanceOfA with { PropB = instanceofA.PropB with { AnotherProp  = "changed" } } 

A related feature that could be useful is to include a reference to the instance being modified within the brackets.

instanceOfA = instanceOfA with { Counter = this.Counter + 1 }

Though arguably even better (for such cases) would be

instanceOfA = instanceOfA with { Counter += 1 }

The this inside the brackets refer to the instanceOfA before assignment. Although in principle it could break some code where this is being used to refer to the instance of the containing class/struct, this type of code is probably very rare (indeed, there are very few cases where one needs to type out "this" when accessing local properties). Alternatively, the compiler could be smart enough to detect ambiguities and issue a warning, falling back to this referring to the containing type as legacy behavior.

[HaloFour]

See: #5176

[dellamonica]

Although that is a nice proposal, it is not a duplicate.

[HaloFour]

I didn't say that it was, although that proposal does cover nearly everything requested here. The one thing it doesn't is the following syntax:

instanceOfA = instanceOfA with { Counter = this.Counter + 1 }

However, this is already legal C# syntax so I don't think it would be possible to interpret as suggested here.

[dellamonica]

Your short reply gave me the impression that you believed it to be a dupe.

Also, I don't see anything in the other proposal about nested records, which is the main proposal here. It would be nice if it could be combined with that proposal.

[HaloFour]

I think that was #77 and I think that was subsumed by #5176, but I could be wrong.

As mentioned in that linked discussion it would be a nice-to-have with property patterns also.

[dellamonica]

Yeah, #77 does cover the nested properties (I think I missed because it is in the "General" category and I was browsing "Language ideas"). Searching for "with" is not very helpful as you can imagine.