lightweight means they have structural equality and are immutable. this is already a huge bonus. microsoft thought people will add methods to them, thus used the class type.

Thanks. I don't really understand what is light about that.

Being able to compare memory to compare two object doesn't make an object any lighter, compared to magically calling a compare method on the object itself (can be decided at compilation time, thus no performance penalty: it depends on what the compare method does.)

Immutability also doesn't make the object lighter, it's again a compile-time property.

I am still missing something...

yeah as said, normally people would see records/data classes as classes that don't use the same amount of memory than a normal class. i.e. some kind of immutable struct. that's why I'm a little bit salty about the feature.

currently records are more comparable to the scala case classes, where you have automatic destructors, better equality, immutability, etc... and not necessary a compacter memory data.

reading the proposal makes more sense than this deep dive, since it explains the reasoning why they don't added special cased data classes.

Previously you had to write a lot of code to implement equality/compare etc.

Records automatically implement them. So its lightweight in that you need less code.

99% of the time when I make a record type with a "with" it's a color, a vector etc. Not sure I really understand why the records can't be either classes or structs.