1, From trait
After you defined the From trait, you can convert a type A to B by calling B::from(A) or B = A.into()
use std::convert::From;
#[derive(Debug)]
struct Number {
num: i32
}
impl From<i32> for Number {
fn from(item: i32) -> Self {
Number {num: item}
}
}
fn main() {
let i = 5;
let num1 = Number::from(i);
let num2: Number = i.into();
println!("num1: {:?}, num2: {:?}", num1, num2);
}
Result:
num1: 5, num2: 5
2, Display & FromStr trait
The Display trait will be used when print an object, e.g. obj.to_string() or println!("{}", obj);
The FromStr will be used when trying to convert a string to the target object with parse() method
use std::fmt;
use std::str::FromStr;
use std::num::ParseIntError;
struct Point {
x: i32,
y: i32,
}
impl fmt::Display for Point {
fn fmt(&self, f:&mut fmt::Formatter) -> fmt::Result {
write!(f, "Point ({}, {})", self.x, self.y)
}
}
impl FromStr for Point {
type Err = ParseIntError;
fn from_str(s: &str) -> Result<Self, Self::Err> {
let tuple: Vec<&str> = s.split(",").collect();
let x = tuple[0].parse::<i32>()?;
let y = tuple[1].parse::<i32>()?;
Ok(Point {x:x, y:y})
}
}
fn main() {
let p1 = Point {x:1, y:2};
let p2: Point = "3,4".parse().unwrap();
println!("P1: {}\nP2: {}", p1, p2);
}
Result:
P1: Point (1, 2)
P2: Point (3, 4)
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