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Update to the foreword

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Bradlee Speice 2019-01-21 13:42:30 -05:00
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14
_drafts/understanding-allocations-in-rust.md
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@ -76,13 +76,18 @@ Now let's address some conditions and caveats before going much further:
(think the [libc] and [winapi] implementations of [malloc]) that we'll ignore. (think the [libc] and [winapi] implementations of [malloc]) that we'll ignore.
- We'll assume a "debug" build of Rust code (what you get with `cargo run` and `cargo test`) - We'll assume a "debug" build of Rust code (what you get with `cargo run` and `cargo test`)
and address (hehe) "release" mode at the end (`cargo run --release` and `cargo test --release`). and address (hehe) "release" mode at the end (`cargo run --release` and `cargo test --release`).
- All content will be run using Rust 1.31, as that's the highest currently supported in the
[Compiler Exporer](https://godbolt.org/). As such, we'll avoid talking about things like
[compile-time evaluation of `static`](https://github.com/rust-lang/rfcs/blob/master/text/0911-const-fn.md)
that are available in nightly.
- Because of the nature of the content, some (very simple) assembly-level code is involved. - Because of the nature of the content, some (very simple) assembly-level code is involved.
We'll keep this to a minimum, but I [needed](https://stackoverflow.com/a/4584131/1454178) We'll keep this to a minimum, but I [needed](https://stackoverflow.com/a/4584131/1454178)
a [refresher](https://stackoverflow.com/a/26026278/1454178) on the `push` and `pop` a [refresher](https://stackoverflow.com/a/26026278/1454178) on the `push` and `pop`
[instructions](http://www.cs.virginia.edu/~evans/cs216/guides/x86.html) [instructions](http://www.cs.virginia.edu/~evans/cs216/guides/x86.html)
while writing this post. while writing this post.
And a final warning worth repeating: And finally, I'll do what I can to flag potential future changes, but the Rust docs
have a notice worth repeating:
> Rust does not currently have a rigorously and formally defined memory model. > Rust does not currently have a rigorously and formally defined memory model.
> >
@ -267,6 +272,13 @@ is almost certainly a code smell.
### **static** ### **static**
Static variables are related to `const` variables, but take a slightly different approach.
When the compiler can guarantee that a *reference* is fixed for the life of a program,
you end up with a `static` variable. Where `const` variables can never change value
(because the value may have been copied to random pieces of code), `static` variables
uniquely identify a location in memory. This allows them to change value under specific
circumstances.
1. What's going on with `lazy_static!()`? 1. What's going on with `lazy_static!()`?
2. What's going on with `thread_local!()`? 2. What's going on with `thread_local!()`?