Class qualifier vs struct qualifier

[Jonathan M Davis]

On Wednesday, June 13, 2018 14:33:48 Jonathan M Davis via Digitalmars-d-
learn wrote:
> On Wednesday, June 13, 2018 07:35:25 RazvanN via Digitalmars-d-learn 
wrote:
> > Hello,
> >
> > I'm having a hard time understanding whether this inconsistency
> > is a bug or intended behavior:
> >
> > immutable class Foo {}
> > immutable struct Bar {}
> >
> > void main()
> > {
> >
> >      import std.stdio : writeln;
> >      Foo a;
> >      Bar b;
> >
> >      writeln("typeof(a): ", typeof(a).stringof);
> >      writeln("typeof(b): ", typeof(b).stringof);
> >
> > }
> >
> > prints:
> >
> > typeof(Foo): Foo
> > typeof(Bar): immutable(Bar)
> >
> >
> > It seems like the class storage class is not taken into account
> > which leads to some awkward situations like:
> >
> > immutable class Foo
> > {
> >
> >      this() {}
> >
> > }
> >
> > void main()
> > {
> >
> >      Foo a = new Foo(); // error: immutable method `this` is not
> >
> > callable using a
> >
> >                         // mutable object
> >
> > }
> >
> > To make it work I have to add immutable to both sides of the
> > expression : immutable Foo a = new immutable Foo(); this is a
> > wonder of redundancy. I already declared the class as immutable
> > so it shouldn't be possible to have mutable instances of it (and
> > it isn't), however I am forced to write the immutable twice even
> > though it is pretty obvious that the class cannot be mutated.
>
> Honestly, from what I understand of how this works, what I find weird is
> the struct case. immutable on classes does _not_ make the class itself
> immutable. It just makes all of its members immutable - hence the error
> about trying to allocate new Foo instead of new immutable Foo. So, that
> is exactly what I would expect. And honestly, being able to write Foo and
> have it imply immutable Foo would get _really_ confusing when reading and
> debugging code.
>
> What's bizarre is that marking the struct with immutable would affect
> anything other than its members.
>
> Bar b;
>
> should not claim that typeof(b) is immutable(Bar). b was not marked as
> immutable. It was listed as Bar, not immutable Bar. So, b shouldn't be
> immutable.

https://issues.dlang.org/show_bug.cgi?id=18977

- Jonathan M Davis