Investigate support for return value bindings

Investigate whether we can simplify function signatures in cases where there is only a single ouput binding. Currently we require an output parameter. In such cases, it would be more natural to simply map the single output binding to the return value of the function.

Note that we already support this as a special case for HttpTrigger. We should investigate whether we can generalize that. In function.json since return values aren’t named in function signatures, we’d have to use a special name like “$return” or something. We also need to think through what this means for script languages like BAT where there is no “return value” for the function.

This would require core SDK changes to support return value attribute binding. E.g.:

[return: Blob("test", FileAccess.Write)]
public static string Test(
    [QueueTrigger("test")] string message)
{
    return "Testing";
}

[mathewc]

FYI: I’m prototyping this now. Basically I’m thinking we can just handle a “$return” output binding specially in our function generation. We map it to normal SDK “out” binding, and simply copy the return value into that out binding after invoking the users function. Meaning we wouldn’t actually have to add this to core SDK, where I don’t think there is much demand for it anyways.

[mathewc]

Guys, take a look at the PR for this referenced above. You can see some example functions in the samples/tests.