On 4/10/18 4:37 AM, David Bennett wrote:
On Tuesday, 10 April 2018 at 08:10:32 UTC, Jonathan M Davis wrote:

Yes. They expect it to work, and as the language is currently designed, it works perfectly well. In fact, it's even built into the language. e.g.

    int[] foo() pure
        return [1, 2, 3, 4];

    void main()
        immutable arr = foo();

compiles thanks to the fact that the compiler can guarantee from the signature of foo that its return value is unique.

Oh is that run at runtime? I thought D was just smart and did it using CTFE.

Well, D could be smart enough and call a runtime function that says it's moving data from thread-local to shared (or vice versa).

We also have std.exception.assumeUnique (which is just a cast to immutable) as a way to document that you're guaranteeing that a reference to an object is unique and therefore can be safely cast to immutable.

Can't say I've used std.exception.assumeUnique, but I guess other people have a use for it as it exists.

Would be nice if you could inject type checking information at compile time without effecting the storage class. But thats a bit OT now.

assumeUnique is a library function, it could be instrumented to do the right thing.

I think it's possible to do this in D, but you need language support.


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