[Proposal]: move parameter modifier

[metaone01]

This is something similar to std::move() in C++. The object's ownership is explicitly transferred into the function. After that, the object should not be used.
move is implicitly including ref.

public class Item : IDisposable {
    ...
}

public void GetOwnership(move IDisposable item) {
    item.Dispose();
}
public void Creator() {
    Item item = new();
    GetOwnership(move item);
    bool use = item.IsDisposed;
//                  ^^^^^^^^^^^
//                  Error: Object's ownership has transferred.
}

I'm not sure if a MoveAttribute is better.

[dlebansais]

I think an attribute would be better because it has a much greater chance to be accepted and a much smaller impact on the ecosystem. You might want to make this suggestion for the runtime instead (asking for a new attribute in the System namespace). You have my support, +10.

[HaloFour]

See: #6612

[metaone01]

It's different.

Introduce a 'move' keyword. 'move' would provide the exact behavior being discussed here: extract some value, zero out the original, and hand back the copied value, similar to the following method:

That 'move' is more like an operator, to move data to another variable and reset the old one.

The object's ownership is explicitly transferred into the function. After that, the object should not be used.

Here, 'move' is a parameter modifier. It is not to move data to another, but to say, "This variable is mine now. You should not use it anymore." It moves the variable's ownership.
After the function invocation, the variable will behave just like it was out of its block scope:

public void Creator() {
    {
        Item item = new();
        // Inline Expansion of GetOwnership(move item);
        item.Dispose();
    }
    bool use = item.IsDisposed; // Error: Cannot resolve symbol 'item'
}

[timcassell]

move is implicitly including ref.

Why? What if I want to move to an async method? That would be illegal.

[metaone01]

You're right. I forgot that.

[metaone01]

Based on the feedback in this discussion, I’ve opened a feature proposal in the dotnet/runtime repo.
Please see: dotnet/runtime#132198

[huoyaoyuan]

API proposals shouldn't be opened at this stage. It should be very late after the C# team has done basic part of the compiler work, and get agreed with the ABI.

[metaone01]

Thank you for the correction. I apologize for opening the issue prematurely — I misunderstood the process. Appreciate your patience, and sorry for the noise.

[metaone01]

And sorry for disturbing—— Could you please transfer this to runtime repo, if it should be?

[huoyaoyuan]

Thank you for the correction. I apologize for opening the issue prematurely — I misunderstood the process. Appreciate your patience, and sorry for the noise.

No worry. It's not something formal. It's just a practical process for attributes associated to the language.

I don't have the permission to transfer. However, the discussion should happen in csharplang repo, because the attribute is going to be used by compiler.

I'd suggest to participate in the design in #10296. It's very closely related to this.