'const' and 'in' parameter storage classes

[ref2401 via Digitalmars-d-learn]

On Friday, 15 May 2015 at 16:08:31 UTC, Adam D. Ruppe wrote:
> The scope storage class means you promise not to escape any 
> reference to the data. This isn't enforced but it is similar in 
> concept to Rust's borrowed pointers - it may someday be 
> implemented to be an error to store them in an outside variable.
>
> Only use 'in' if you are looking at the data, but not modifying 
> or storing copies of pointers/references to it anywhere in any 
> way.

I expected the compiler forbids 'in' params escaping.

struct MyStruct {
	this(int a) {
		this.a = a;
	}

	int a;
}


const(MyStruct)* globalPtr;

void main(string[] args) {
	MyStruct ms = MyStruct(10);

	foo(ms);
	ms.a = 12;

	writeln("global: ", *globalPtr); // prints const(MyStruct)(12)
}

void foo(in ref MyStruct ms) {
	globalPtr = &ms; // is it legal?
}