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Rollup merge of #22911 - djmally:master, r=steveklabnik

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... example that actually does use an Option
This commit is contained in:
Manish Goregaokar 2015-03-02 13:38:50 +05:30
commit 16efd0ecbf
1 changed files with 9 additions and 9 deletions
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18
src/doc/trpl/guessing-game.md
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@ -422,11 +422,11 @@ In this case, we say `x` is a `u32` explicitly, so Rust is able to properly
tell `random()` what to generate. In a similar fashion, both of these work:
```{rust,ignore}
let input_num = "5".parse::<u32>(); // input_num: Option<u32>
let input_num: Result<u32, _> = "5".parse(); // input_num: Result<u32, <u32 as FromStr>::Err>
let input_num_option = "5".parse::<u32>().ok(); // input_num: Option<u32>
let input_num_result: Result<u32, _> = "5".parse(); // input_num: Result<u32, <u32 as FromStr>::Err>
```
Here we're converting the `Result` returned by `parse` to an `Option` by using
Above, we're converting the `Result` returned by `parse` to an `Option` by using
the `ok` method as well. Anyway, with us now converting our input to a number,
our code looks like this:
@ -470,14 +470,14 @@ Let's try it out!
```bash
$ cargo build
Compiling guessing_game v0.0.1 (file:///home/you/projects/guessing_game)
src/main.rs:22:15: 22:24 error: mismatched types: expected `u32` but found `core::option::Option<u32>` (expected u32 but found enum core::option::Option)
src/main.rs:22 match cmp(input_num, secret_number) {
src/main.rs:21:15: 21:24 error: mismatched types: expected `u32`, found `core::result::Result<u32, core::num::ParseIntError>` (expected u32, found enum `core::result::Result`) [E0308]
src/main.rs:21 match cmp(input_num, secret_number) {
^~~~~~~~~
error: aborting due to previous error
```
Oh yeah! Our `input_num` has the type `Option<u32>`, rather than `u32`. We
need to unwrap the Option. If you remember from before, `match` is a great way
Oh yeah! Our `input_num` has the type `Result<u32, <some error>>`, rather than `u32`. We
need to unwrap the Result. If you remember from before, `match` is a great way
to do that. Try this code:
```{rust,no_run}
@ -500,7 +500,7 @@ fn main() {
let input_num: Result<u32, _> = input.parse();
let num = match input_num {
Ok(num) => num,
Ok(n) => n,
Err(_) => {
println!("Please input a number!");
return;
@ -524,7 +524,7 @@ fn cmp(a: u32, b: u32) -> Ordering {
}
```
We use a `match` to either give us the `u32` inside of the `Option`, or else
We use a `match` to either give us the `u32` inside of the `Result`, or else
print an error message and return. Let's give this a shot:
```bash