D 2015/2016 Vision?

[Namespace via Digitalmars-d]

On Monday, 5 October 2015 at 19:07:20 UTC, Meta wrote:
> On Monday, 5 October 2015 at 17:19:09 UTC, Gary Willoughby 
> wrote:
>> This can be shortened to:
>>
>> import std.stdio;
>> import std.typecons;
>>
>> class A
>> {
>> 	string name;
>>
>> 	this(string name)
>> 	{
>> 		this.name = name;
>> 	}
>>
>> 	void hello()
>> 	{
>> 		writeln("Hello, ", this.name);
>> 	}
>> }
>>
>> void main()
>> {
>> 	auto a = scoped!A("Foo");
>> 	a.hello();
>> }
>
> There's a critical flaw in `scoped`. Observe:
>
> import std.stdio;
> import std.typecons;
>
> class A
> {
> 	string name;
>
> 	this(string name)
> 	{
> 		this.name = name;
> 		writeln("Creating A");
> 	}
>
> 	~this()
> 	{
> 		writeln("Destroying A");
> 	}
>
> 	void hello()
> 	{
> 		writeln("Hello, ", this.name);
> 	}
> }
>
> void main()
> {
> 	auto a1 = scoped!A("Foo");
> 	a1.hello();
>
> 	A a2 = scoped!A("Foo");
> 	a2.hello();
> }
>
>
> The output:
>
> Creating A
> Hello, Foo
> Creating A
> Destroying A
> Destroying A
> object.Error: Access Violation

----
import std.stdio;

struct Scoped(T) {
	void[__traits(classInstanceSize, T)] buf = void;
	
	this(Args...)(auto ref Args args) {
		this.buf = typeid(T).init[];
		(cast(T) this.buf.ptr).__ctor(args);
	}
	
	~this() {
		.destroy(this.get());
	}
	
		
	T get() {
		return cast(T) this.buf.ptr;
	}
	
	alias get this;
}

auto scoped(T, Args...)(auto ref Args args) {
	return Scoped!T(args);
}

class A
{
     string name;

     this(string name)
     {
        this.name = name;
        writeln("Creating A");
     }

     ~this()
     {
        writeln("Destroying A");
     }

     void hello()
     {
        writeln("Hello, ", this.name);
     }
}

void main() {
	auto a1 = scoped!A("Foo");
	a1.hello();
	
	auto a2 = scoped!A("Bar");
	a2.hello();
}
----

Application output:
Creating A
Hello, Foo
Creating A
Hello, Bar
Destroying A
Destroying A