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More edits and some TODOs for strings

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Carol (Nichols || Goulding) 2016-09-19 22:37:06 -04:00
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@ -250,6 +250,8 @@ should `answer` be `208`? `208` is not a valid character on its own, though.
Plus, for latin letters, this would not return the answer most people would Plus, for latin letters, this would not return the answer most people would
expect: `&"hello"[0]` would then return `104`, not `h`. expect: `&"hello"[0]` would then return `104`, not `h`.
### Bytes, and Scalar Values, and Grapheme Clusters! Oh my!
This leads to another point about UTF-8: there are really three relevant ways This leads to another point about UTF-8: there are really three relevant ways
to look at strings, from Rust's perspective: bytes, scalar values, and grapheme to look at strings, from Rust's perspective: bytes, scalar values, and grapheme
clusters. If we look at the string "नमस्ते", it is ultimately stored as a `Vec` clusters. If we look at the string "नमस्ते", it is ultimately stored as a `Vec`
@ -281,10 +283,11 @@ really complicated yet?
All of these problems mean that Rust does not implement `[]` for `String`, so All of these problems mean that Rust does not implement `[]` for `String`, so
we cannot directly do this. we cannot directly do this.
However. ## Slicing Strings
Sometimes, indexing the bytes of a string is useful. So while you can't use `[]` However, indexing the bytes of a string is very useful. While you can't use
with a single number, you _can_ use `[]` with a range: `[]` with a single number, you _can_ use `[]` with a range to create a string
slice from particular bytes:
```rust ```rust
let hello = "Здравствуйте"; let hello = "Здравствуйте";
@ -294,8 +297,19 @@ let s = &hello[0..4];
Here, `s` will be a `&str` that contains the first four bytes of the string. Here, `s` will be a `&str` that contains the first four bytes of the string.
Earlier, we mentioned that each of these characters was two bytes, so that means Earlier, we mentioned that each of these characters was two bytes, so that means
that `s` will be 'Зд'. that `s` will be "Зд".
What would happen if we did `&hello[0..1]`? We said each of these characters What would happen if we did `&hello[0..1]`? We said each of these characters
required two bytes. The answer: it will panic, in the same way that accessing required two bytes. The answer: it will panic at runtime, in the same way that
an invalid index in a vector does. accessing an invalid index in a vector does:
```bash
thread 'main' panicked at 'index 0 and/or 1 in `Здравствуйте` do not lie on
character boundary', ../src/libcore/str/mod.rs:1694
```
## Methods for Iterating Over Strings
TODO: Add examples of using `bytes`, `chars`, since those are recommended?
TODO: summary that ties this to the next chapter