Re: Private enum members + Descent

[Lars T. Kyllingstad]

Yigal Chripun wrote:
On 26/10/2009 12:07, Lars T. Kyllingstad wrote:
Yigal Chripun wrote:
personally I'd like to see D enums replaced by Java style enums which
make more sense to me. D enums are even worse than C enums since you
can write:
enum foo = "text";
which to me looks very similar to:
auto cat = new Dog;


I agree that enum is a horrible keyword to use for declaring manifest
constants. In my opinion the D developers are sometimes a bit too afraid
of introducing new keywords, and this is one of the consequences.

Personally, I think this would be a better scheme:

const: manifest constants, no storage (like const in D1, enum in D2)
readonly: used for a read-only view of mutable data (like const in D2)
immutable: truly immutable data (like now)

-Lars

i don't think we need to add more options, I think we need to remove 
options.
there should be only two types, const and mutable.
manifest constants should be a linker optimization and immutable is only 
relevant as part of a concurrency model and even then there's no need 
for a separate keyword.

immutable objects are shared objects where only the owner is allowed to 
modify it and only if it's done in a thread-safe way (synchronized with 
locks, lock-free algorithms).
void foo() {
// can be optimized away (transformed into a manifest constant)
// taking address of var is illegal
const var = 42;
// allocated on the heap and you can pass it's address around
auto bar = new const int(42);
}


I was going to protest: "But what about const struct members? Should the 
size of the following struct depend on whether the compiler determines 
it can optimize by turning its const member into a manifest constant?"

  struct Foo { const int bar = 123; }

But then I decided to actually try it with the current DMD2, and found 
that the compiler does just that!

  writeln(Foo.sizeof);    // Prints "1", not "4"

  Foo foo;
  auto p = &foo.bar;   // Error: constant 123 is not an lvalue

What's going on? Is this intended behaviour?

-Lars