Inline Classes and extends

John Rose john.r.rose at
Tue Dec 10 18:21:15 UTC 2019

On Dec 10, 2019, at 10:17 AM, August Nagro <augustnagro at> wrote:
> One question I have is about `extends`. I understand that inline classes cannot extend IdentityClass, but what about other inline classes? I have a lot of classes that would make sense as inline, but are held back by their superclass (which also could be inline).

One thing you get with the extra indirection of reference objects
is layout polymorphism, the power to have one type which points
at two or more distinct layouts.

If you get rid of the pointer (which is a must for inlines, so they
can “work like an int”), then you also lose the ability to represent
layout polymorphism.

It’s like in C++ when you try to mix inheritance and by-value storage
of instances:  Stuff goes wrong, awkwardly.

struct A { int x; }
struct B : public A { int y; }
A avar; avar.x = 1;
B bvar; bvar.x = 2; bvar.y = 3;
A anotheravar = bvar;  // what happened to the 3??

— John

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