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Rustlings: if 編

Rust
tarotenetarotene

何となくハンズオン形式の学習コンテンツは記事ではなくスクラップの方が良さげなので，if 編から試験的にスクラップを運用してみる．

tarotenetarotene

Debugging if1.rs 

⚠️  Compiling of exercises/if/if1.rs failed! Please try again. Here's the output:
error[E0308]: mismatched types
 --> exercises/if/if1.rs:5:34
  |
5 | pub fn bigger(a: i32, b: i32) -> i32 {
  |        ------                    ^^^ expected `i32`, found `()`
  |        |
  |        implicitly returns `()` as its body has no tail or `return` expression

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
tarotenetarotene

急に趣向が変わった:

./exercises/if/if1.rs より抜粋
pub fn bigger(a: i32, b: i32) -> i32 {
    // Complete this function to return the bigger number!
    // Do not use:
    // - another function call
    // - additional variables
    // Execute `rustlings hint if1` for hints
}

穴埋め問題か．単に完成されてないからビルドエラーが出るケース．

tarotenetarotene

外部関数の呼び出しと新しい変数宣言は禁止，がレギュレーションか．

tarotenetarotene

何も考えずに

pub fn bigger(a: i32, b: i32) -> i32 {
    if (a > b) {
        return a;
    } else {
        return b;
    }
}

でいったら通った．ちなみに Rust には三項演算子（ternary operator）はないそう．

tarotenetarotene

Debugging if2.rs 

⚠️  Compiling of exercises/if/if2.rs failed! Please try again. Here's the output:
error[E0308]: mismatched types
  --> exercises/if/if2.rs:13:9
   |
13 |         1
   |         ^ expected `&str`, found integer

error: aborting due to previous error

For more information about this error, try `rustc --explain E0308`.
tarotenetarotene

単に if else の条件分岐で異なる型を出し分けているだけ，なので &str に揃える．

tarotenetarotene
⚠️  Testing of exercises/if/if2.rs failed! Please try again. Here's the output:

running 3 tests
test tests::foo_for_fizz ... ok
test tests::bar_for_fuzz ... FAILED
test tests::default_to_baz ... FAILED

successes:

successes:
    tests::foo_for_fizz

failures:

---- tests::bar_for_fuzz stdout ----
thread 'tests::bar_for_fuzz' panicked at 'assertion failed: `(left == right)`
  left: `"1"`,
 right: `"bar"`', exercises/if/if2.rs:29:9
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

---- tests::default_to_baz stdout ----
thread 'tests::default_to_baz' panicked at 'assertion failed: `(left == right)`
  left: `"1"`,
 right: `"baz"`', exercises/if/if2.rs:34:9


failures:
    tests::bar_for_fuzz
    tests::default_to_baz

test result: FAILED. 1 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s

初めてテスト結果らしきものを見た気がする．

tarotenetarotene

bar_for_fuzz および default_to_baz のアサーションでコケてそうなので丁寧に眺める．

tarotenetarotene

テストコードは

#[test]
fn bar_for_fuzz() {
    assert_eq!(fizz_if_foo("fuzz"), "bar")
}

#[test]
fn default_to_baz() {
    assert_eq!(fizz_if_foo("literally anything"), "baz")
}

なので，これに合わせて実装を変更．

tarotenetarotene

次回予告: quit 編に突入

⚠️  Compiling of exercises/quiz1.rs failed! Please try again. Here's the output:
error[E0425]: cannot find function `calculate_apple_price` in this scope
  --> exercises/quiz1.rs:18:18
   |
18 |     let price1 = calculate_apple_price(35);
   |                  ^^^^^^^^^^^^^^^^^^^^^ not found in this scope

error[E0425]: cannot find function `calculate_apple_price` in this scope
  --> exercises/quiz1.rs:19:18
   |
19 |     let price2 = calculate_apple_price(40);
   |                  ^^^^^^^^^^^^^^^^^^^^^ not found in this scope

error[E0425]: cannot find function `calculate_apple_price` in this scope
  --> exercises/quiz1.rs:20:18
   |
20 |     let price3 = calculate_apple_price(65);
   |                  ^^^^^^^^^^^^^^^^^^^^^ not found in this scope

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0425`.

何かめっちゃ出てるけど見掛け倒しっぽいな．

このスクラップは2022/03/25にクローズされました