Add proxy class that can implement interfaces at runtime.

[justinfagnani]

In unchecked mode it's possible to create objects that implement an interface via noSuchMethod and assign them to a variable or argument of the interface type. This is useful for things like typed proxies for JS interop, automatic stubs for remote/isolated services, etc. In checked mode though assigning to a typed variable causes an exception.

For Proxy, this should work:

var proxy = new Proxy([Foo, Bar]);
assert(proxy is Bar);
assert(proxy is Foo);

Then subclasses can implement behavior.

[gbracha]

We are aware of this issue and intend to resolve it, as these usage patterns are very important. The specific solution suggested here may or may not be what we end up doing.

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Set owner to @gbracha.
Added Accepted label.

[DartBot]

This comment was originally written by [email protected]

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Is there any progress on this matter?

I use this pattern a lot in my code. For now I do a workaround and introduce a new class for every proxied class but that's cumbersome.

For me to invest more in the dart language, I need to be sure that this is gonna be implemented somehow at some point in the (near) future.

[floitschG]

Issue #6244 has been merged into this issue.

[justinfagnani]

Added C1 label.

[DartBot]

This comment was originally written by [email protected]

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IMO related:

• Issue Allow exempting parts of the program (especially external library calls) from type checking while running in checked mode #16638 Allow fine grain control over checked-mode behavior in production and development; Issue Allow fine grain control over checked-mode behavior in production and development #18138
• and possibly Issue Contracts #3049 Contracts; Issue Structural types #21984 Structural types

[pulyaevskiy]

Hey team, just curious, the fact that it's not accepted anymore means this will not be implemented?

I am really interested in solution for this use case.

[floitschG]

@pulyaevskiy:
Sorry for the late response.
As long as the bug is open, it hasn't been rejected. It's not yet high on our TODO lists, and, even when accepted, the outcome might look very different from the proposal here.

TL;DR: we see the need, but we are not currently working on it.