> If the allocation is hidden to the programmer, she might not realize the expensive operations behind the scenes.
I am a green Rust programmer, and I currently have little insight into the allocation costs of the various things I'm doing, and I haven't yet found a strategy for gaining it. I feel like the actual mechanisms for memory management are so deeply buried that it would take lots and lots of spelunking to get an idea of what's going on behind the scenes. Even something as simple as a "This function allocates <x> memory" tag with stdlib functions would help me immensely.
I agree that we should add some more documentation in this area (though we always have to be careful that we don't document things so thoroughly that we de-facto stabilize the internals and make it impossible for us to improve them in the future). But in the meantime, if you're just learning the language, I would recommend not being overly concerned with the performance details of collections until you start seeing them at the top of your performance profiles.
EDIT: And of course, I do encourage you to check out the documentation that we have in the std::collections module that goes into at least a little detail about each of the standard collections, along with tips for choosing when to use each: https://doc.rust-lang.org/std/collections/#when-should-you-u...
Well, it's not so much about performance of existing code as it is about being able to take a high-level view of the design of a program. To pick a bad example, if I know one function will allocate memory according to a certain pattern (e.g. 2n*sizeof(obj)) and another will just shift an internal pointer around, I predict it'll get easier to reason about the behavior of the code. The semantics of ?alloc+free are exceptionally easy to understand, but I have no idea how or when Rust allocates memory, except for a vague notion of heap vs stack. I suspect there's an elegant relationship between how Rust does its (hidden) memory management and the behavior of the borrow checker, but I haven't come across anything yet linking the two concepts.
Mostly, I think my problem is that I don't know what I don't know. Like I said, I'm green. :)
I am interested in improving this. It's tough because as an experienced Rust programmer, I feel like it's obvious, but have a hard time figuring out how to put it into words. It should be something that can be intuitive, rather than needing explicit docs, though those can help too.
> If the allocation is hidden to the programmer, she might not realize the expensive operations behind the scenes.
I am a green Rust programmer, and I currently have little insight into the allocation costs of the various things I'm doing, and I haven't yet found a strategy for gaining it. I feel like the actual mechanisms for memory management are so deeply buried that it would take lots and lots of spelunking to get an idea of what's going on behind the scenes. Even something as simple as a "This function allocates <x> memory" tag with stdlib functions would help me immensely.