161 lines
4.3 KiB
Markdown
161 lines
4.3 KiB
Markdown
# Getting Started
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These exercises lean on Test-Driven Development (TDD), but they're not
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an exact match.
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The following steps assume that you are in the same directory as the exercise.
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You must have rust installed.
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Follow the [Installing Rust chapter in the Rust book](http://doc.rust-lang.org/stable/book/installing-rust.html).
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The [getting started with rust](http://help.exercism.io/getting-started-with-rust.html)
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section from exercism is also useful.
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## Step 1
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Run the test suite. It can be run with `cargo`, which is installed with rust.
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```
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$ cargo test
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```
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This will fail, complaining that `hello-world` could not compile.
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To fix this, create a new directory called `src`.
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Create a new file called, `lib.rs`, inside the `src` directory.
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## Step 2
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Run the test again. It will give you a new error, another compile error.
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Our `lib.rs` does not contain any code, specifically the `hello()`
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function that our test is looking for.
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### Fixing the Error
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To fix it, open up the `src/lib.rs` file and add the following code:
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```rust
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pub fn hello(name: Option<&str>) -> String {
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"".to_string()
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}
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```
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Our test is looking for the `hello()` function from the `hello_world`
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crate. `lib.rs`, by default, is our crate root and our test
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is looking for the `hello()` function there.
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The code we are adding to `lib.rs` defines a public function (`pub fn`) that is called "hello".
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The function accepts a `name` as an optional argument (`Option`).
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The function returns a `String`.
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We start by returning an empty string (`"".to_string()`).
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## Step 3
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Run the test again.
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This time, code compilation will pass and we receive actual test failures.
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```
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running 3 tests
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test test_other_same_name ... ignored
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test test_sample_name ... ignored
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test test_no_name ... FAILED
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failures:
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---- test_no_name stdout ----
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thread 'test_no_name' panicked at 'assertion failed: `(left == right)`
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(left: `"Hello, World!"`, right: `""`)', tests/hello-world.rs:5
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failures:
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test_no_name
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test result: FAILED. 0 passed; 1 failed; 2 ignored; 0 measured
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```
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### Understanding Test Failures
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Only one of the tests runs (`test_no_name`) and it fails. The other
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tests are ignored (more on that later).
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The `test_no_name` failure states that it is expecting the value,
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`"Hello, World!"`, to be returned from `hello("")`.
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The left side of the assertion (at line 5) should be equal to the right side.
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```
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---- test_no_name stdout ----
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thread 'test_no_name' panicked at 'assertion failed: `(left == right)`
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(left: `"Hello, World!"`, right: `""`)', tests/hello-world.rs:5
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```
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To fix it, let's return `"Hello, World!"`, instead of an empty string
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(`""`) inside our `hello` function.
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```rust
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pub fn hello(name: Option<&str>) -> String {
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"Hello, World!".to_string()
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}
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```
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## Step 4
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Run the test again. This time, it will pass.
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```
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running 3 tests
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test test_other_same_name ... ignored
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test test_sample_name ... ignored
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test test_no_name ... ok
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test result: ok. 1 passed; 0 failed; 2 ignored; 0 measured
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Doc-tests hello-world
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running 0 tests
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test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured
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```
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You may have noticed compiler warnings earlier:
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```
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Compiling hello-world v0.0.0
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(file:////exercism/exercises/rust/hello-world)
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src/lib.rs:1:14: 1:18 warning: unused variable: `name`, #[warn(unused_variables)] on by default
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src/lib.rs:1 pub fn hello(name: Option<&str>) -> String {
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^~~~
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```
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Our `hello` function does not use the `name` argument so the
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compiler is letting us know that we could potentially remove the
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argument from our function (it likes "clean code").
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As we make the rest of the tests pass, we will find that we need the `name`
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argument, so don't delete it.
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Activate the next test. Open the `tests/hello-world.rs` file.
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Delete the `#[ignore]` line for the `test_sample_name` test.
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## Step 5
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Run the test suite again. Read the test failure and make the test pass.
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As a reminder, the [rust book](http://doc.rust-lang.org/stable/book/README.html)
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is a good reference for understanding rust.
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The cargo output may also have hints to help you, depending on the errors you get.
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For example, `rustc --explain E0425` will explain unresolved name errors.
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## Wash, Rinse, Repeat
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Delete one `#[ignore]` at a time, and make each test pass before you move to
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the next one.
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## Submit
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When everything is passing, you can submit your code with the following
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command:
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```
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$ exercism submit src/lib.rs
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```
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