【Rust日报】2020-01-25 Rust 2020 路线图，typed-builder，format!

#[macro_use]
extern crate typed_builder;

#[derive(TypedBuilder)]
struct Foo {
    // Mandatory Field:
    x: i32,

    // #[builder(default)] without parameter - use the type's default
    // #[builder(setter(strip_option))] - wrap the setter argument with `Some(...)`
    #[builder(default, setter(strip_option))]
    y: Option<i32>,

    // Or you can set the default
    #[builder(default=20)]
    z: i32,
}

Foo::builder().x(1).y(2).z(3).build();
Foo::builder().z(1).x(2).y(3).build();

Foo::builder().x(1).build();

Foo::builder().build(); // missing x
Foo::builder().x(1).y(2).y(3); // y is specified twice

format!("Hello");                 // => "Hello"
format!("Hello, {}!", "world");   // => "Hello, world!"
format!("The number is {}", 1);   // => "The number is 1"
format!("{:?}", (3, 4));          // => "(3, 4)"
format!("{value}", value=4);      // => "4"
format!("{} {}", 1, 2);           // => "1 2"
format!("{:04}", 42);             // => "0042" with leading zeros