fix some typos
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@ -42,7 +42,7 @@ fn main() {
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// The problem with `derive` is there is no control over how
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// the results look. What if I want this to just show a `7`?
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/* Make it output: Now 7 will print! */
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/* Make it print: Now 7 will print! */
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println!("Now {:?} will print!", Deep(Structure(7)));
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}
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```
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@ -69,10 +69,46 @@ impl fmt::Debug for Point2D {
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}
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fn main() {
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let point = Point2D { x: 3.3, y: 7.2 };
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println!("{}", point);
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println!("{:?}", point);
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assert_eq!(format!("{}",point), "Display: 3.3 + 7.2i");
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assert_eq!(format!("{:?}",point), "Debug: Complex { real: 3.3, imag: 7.2 }");
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println!("Success!")
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}
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```
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5.
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```rust
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use std::fmt; // Import the `fmt` module.
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// Define a structure named `List` containing a `Vec`.
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struct List(Vec<i32>);
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impl fmt::Display for List {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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// Extract the value using tuple indexing,
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// and create a reference to `vec`.
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let vec = &self.0;
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write!(f, "[")?;
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// Iterate over `v` in `vec` while enumerating the iteration
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// count in `count`.
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for (count, v) in vec.iter().enumerate() {
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// For every element except the first, add a comma.
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// Use the ? operator to return on errors.
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if count != 0 { write!(f, ", ")?; }
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write!(f, "{}: {}",count, v)?;
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}
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// Close the opened bracket and return a fmt::Result value.
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write!(f, "]")
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}
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}
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fn main() {
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let v = List(vec![1, 2, 3]);
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assert_eq!(format!("{}",v), "[0: 1, 1: 2, 2: 3]");
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}
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```
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@ -67,7 +67,7 @@ fn main() {
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// The problem with `derive` is there is no control over how
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// the results look. What if I want this to just show a `7`?
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/* Make it output: Now 7 will print! */
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/* Make it print: Now 7 will print! */
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println!("Now {:?} will print!", Deep(Structure(7)));
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}
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```
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@ -81,6 +81,8 @@ Anotherthing to note: the placefolder for `Display` is `{}` not `{:?}`.
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4. 🌟🌟
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```rust,editable
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/* Make it work*/
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use std::fmt;
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struct Point2D {
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@ -97,31 +99,27 @@ impl fmt::Debug for Point2D {
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}
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fn main() {
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let point = Point2D { x: 3.3, y: 7.2 };
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/* Make it output:
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Display: 3.3 + 7.2i
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*/
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println!("{}", point);
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/* Make it output:
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Debug: Complex { real: 3.3, imag: 7.2 }
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*/
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println!("{:?}", point);
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assert_eq!(format!("{}",point), "Display: 3.3 + 7.2i");
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assert_eq!(format!("{:?}",point), "Debug: Complex { real: 3.3, imag: 7.2 }");
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println!("Success!")
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}
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```
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### Example
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### `?` operator
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Implementing `fmt::Display` for a structure whose elements must be handled separately is triky. The problem is each `write!` generates a `fmt::Result` which must be handled in the same place.
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Fortunately, Rust provides the `?` operator to help us eliminate some unnecessary codes for deaing with `fmt::Result`.
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5. 🌟🌟
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```rust,editable
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use std::fmt; // Import the `fmt` module.
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// Define a structure named `List` containing a `Vec`.
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/* Make it work */
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use std::fmt;
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struct List(Vec<i32>);
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impl fmt::Display for List {
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@ -148,7 +146,8 @@ impl fmt::Display for List {
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fn main() {
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let v = List(vec![1, 2, 3]);
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println!("{}", v);
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assert_eq!(format!("{}",v), "[0: 1, 1: 2, 2: 3]");
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println!("Success!")
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}
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```
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