Expliciting lifetime in the first example #351
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The main issue with having three lets one after the other, is that it's not clear if the lifetime created due to `let x` is the one before or after this line. Assuming I understood correctly what's going on, this example will clarify that the lifetime is created after the let. I also add a note stating what the usual notation is and warning that this longer explicit lifetime name is used only once for the sake of being as clear as possible. Other solutions I considered would be to add a "print" between two lets, this will ensure that the lifetime introduction is near a single "let", hence making it clear which "let" is concerned by the lifetime. If I got it wrong and actually the scope is introduced before the let statement, I guess at least this confirms that clarification may be helpful.
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I've read the book, and I must admit that, as far as I understand, it did not go in such gritty details as to indicate whether the lifetime technically starts before or after a variable declaration. Not that this distinction seemed useful in normal use of rust as far as I understand. Would it be okay to not only state that 'a is global, but
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Co-authored-by: Yuki Okushi <[email protected]>
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I beg your pardon, does "waiting-on-review" mean you wait for another reviewer, or that you wait for me to do a change? |
| Wow. That's... awful. Let's all take a moment to thank Rust for making this | ||
| easier. To make matter worse, traditionally, lifetimes are not as descriptive | ||
| and simply called `'a`, `'b`, and so on. We will respect this tradition going | ||
| forward. |
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I don't think this change is much helpful for readers and worth rephrasing so. As stated in the intro, we assume readers have a basic knowledge of Rust, actually, https://doc.rust-lang.org/nightly/book/ch10-03-lifetime-syntax.html#lifetime-annotation-syntax explains it and that should be enough.
| // NOTE: `'a: {` and `&'b x` is not valid syntax! | ||
| 'a: { | ||
| // NOTE: `'global_lifetime: {` and `&'x_lifetime x` is not valid syntax! | ||
| 'global_lifetime: { | ||
| let x: i32 = 0; | ||
| 'b: { | ||
| // lifetime used is 'b because that's good enough. | ||
| let y: &'b i32 = &'b x; | ||
| 'c: { | ||
| // ditto on 'c | ||
| let z: &'c &'b i32 = &'c y; | ||
| 'x_lifetime: { | ||
| // lifetime used is 'x_lifetime because that's good enough. | ||
| let y: &'x_lifetime i32 = &'x_lifetime x; | ||
| 'y_lifetime: { | ||
| // ditto on 'y_lifetime | ||
| let z: &'y_lifetime &'x_lifetime i32 = &'y_lifetime y; |
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After some re-thinking of this, I still think this is too descriptive. We easily can find 'a is a lifetime and curly braces are scopes if we're familiar with Rust's syntax. That is, naming lifetimes looks redundant, and tweaking prior wording should be enough here.
It implies a PR is waiting on review. I was going to do a second review. |
The main issue with having three lets one after the other, is that it's not
clear if the lifetime created due to
let xis the one before or after thisline. Assuming I understood correctly what's going on, this example will clarify
that the lifetime is created after the let. I also add a note stating what the
usual notation is and warning that this longer explicit lifetime name is used
only once for the sake of being as clear as possible.
Other solutions I considered would be to add a "print" between two lets, this
will ensure that the lifetime introduction is near a single "let", hence making
it clear which "let" is concerned by the lifetime.
If I got it wrong and actually the scope is introduced before the let statement,
I guess at least this confirms that clarification may be helpful.
If the sake of clarity is more important than the sake of tradition, I'm willing to spend the time needed to add more explicit lifetime name to the other examples