From the motivation section:

> So you want to invoke a method X in a library that later calls back into your 
> code. In your callback you need some context, perhaps a transaction ID or 
> some File instances. However, X provides no way to pass a reference through 
> their code into your callback. What are you to do?

When I read this, my first thought was… pass a callback that is bound to the 
context.

I suppose the example you have in mind has a fixed callback. Is this a common 
practice? Doesn’t it point to a deficiency in the library API?

Is this feature just a workaround for poorly designed libraries, or are there 
other examples?

  Alan

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