classes by value

[Petar]

On Thursday, 14 December 2017 at 16:10:17 UTC, Jonathan Marler 
wrote:
> On Thursday, 14 December 2017 at 14:45:51 UTC, Dgame wrote:
>> Strongly reminds me of scoped
>
> Declaring a variable as `scoped` prevents that variable from 
> escaping the scope it is declared in.  This restriction allows 
> the compiler certain optimizations, such as allocating classes 
> on the stack, i.e.
> ```
> scoped foo = new Foo();
> ```
>
> this optimization is well-known to D programmers so class 
> allocation on the stack is strongly associated with the 
> "scoped" modifier which is probably why this "class by value" 
> snippet reminds you of "scoped".
>
> Even though "classes by value" can be implied in certain usages 
> of "scoped", "scoped" carries with it extra semantics that 
> "classes by value" on it's own does not. This snippet allows 
> "classes by value" on it's own, which enables different ways of 
> using classes (for example, creating an array of classes by 
> value `Value!MyClass[]`).

I think what Dgame meant was: 
https://dlang.org/phobos-prerelease/std_typecons#scoped. For the 
built-in scoped classes, the keyword is 'scope', not 'scoped': 
https://dlang.org/spec/class.html#auto.

So you can have both:

```
scope foo = new Foo();
```

and:
```
auto foo = scoped!Foo();
```

and finally:
```
scope foo = scoped!Foo();
```