C# js-like spread (or triple dot) operator [duplicate]

I need to copy all properties of an object into anonymous object. In JavaScript I'd do it the following way:

items.map(item => ({...item, extra = 'additional property'}))

In C# I would have to copy property by property:

items.Select(item => new { item.Prop1, item.Prop2, Extra = "additional property" })

Or alternatively I'd use reflection and ExpandoObject. Any other thoughts?