Add Disposable.isDisposable

[as-cii]

So that we can check whether an object correctly implements the Disposable contract, as discussed in #12.

/cc: @maxbrunsfeld @nathansobo @kevinsawicki

[maxbrunsfeld]

Usually we don't denote these class methods w/ the ::, because that's coffee-script notation for referring to properties on a prototype.

[as-cii]

Sounds good, I had a look at how we did it in text-buffer and I mistakenly assumed it was a standard to refer to every kind of method.

Thanks for pointing this out! 👍

[maxbrunsfeld]

Other than the one comment, looks good to me! Thanks for doing this.

[mnquintana]

Is the existential operator needed here? It might be useful to blow up if you're accidentally passing in a null or undefined object

[maxbrunsfeld]

Generally, I could go either way, but I think it's good to imitate Array.isArray, Number.isNaN et al in this case. They return false when passed null or undefined.

[maxbrunsfeld]

🚢

[as-cii]

❤️

[nathansobo]

I like this approach. Less obtrusive.