TRPL: Drop

[steveklabnik]

r? @alexcrichton

[alexcrichton]

Nice! I was almost quite surprised at how short this was, so I'm curious, but what do you think about discussing topics like:

• Common usage patterns of destructors, including: writing FFI bindings which clean up owned resources, making a destructor run in linear time when it would otherwise be recursive (e.g. a BST), or some sort of "bomb" which does something (e.g. a profiling timer that registers info when it goes out of scope.
• Hazards of destructors not possibly running in all circumstances (ala mem::forget) and possible intentional use cases of canceling a destructor.
• Interaction between Drop and Copy
• Interaction of RAII and Drop

etc.

[steveklabnik]

I wasn't sure how far to go, exactly, and didn't want this to be a TODO :)

I'm open to some of this for now, and more later. Basically, I'm mostly focused on getting tutorials done for friday's release, but some of this will be quick to add and have a lot of value. I'll update it later tonight and ping you again :)

[Gankra]

This seems a tad awkward. It is definitely also used for cleaning up memory (std::boxed::*, std::rc::*std::collections::*, ...).

[steveklabnik]

yeah, i'll remove that

[steveklabnik]

@alexcrichton so, in the interest of getting the basics in before the deadline, I'm thinking about leaving that to future work, and just merging what I have now. What do you think?

[pnkfelix]

For future reference for the future work: I do so enjoy examples of using Drop to instrument dynamic behavior, like the test I wrote up here:

https://raw.githubusercontent.com/rust-lang/rust/master/src/test/run-pass/issue-23338-ensure-param-drop-order.rs

(expurgiated playpen version here too, so you can run it directly from the browser and see the cool output)

[pnkfelix]

On a more serious note: I think Knuth uses an "under construction" icon for sections of his text that he knows will be undergoing expansion or revision in the next edition of his text. Maybe you should consider doing something similar, so that the reader knows that there is more to be learned on the topic, and that they are encouraged to ask around in the community about it?

[steveklabnik]

@pnkfelix i like that idea, for sure.

[alexcrichton]

@bors: r+ 9a3e98b rollup