pub fn default<T>() -> T where T: Default,
Return the default value of a type according to the Default trait.
The type to return is inferred from context; this is equivalent to Default::default() but shorter to type.
For example:
#![feature(default_free_fn)]
use std::default::default;
#[derive(Default)]
struct AppConfig {
    foo: FooConfig,
    bar: BarConfig,
}
#[derive(Default)]
struct FooConfig {
    foo: i32,
}
#[derive(Default)]
struct BarConfig {
    bar: f32,
    baz: u8,
}
fn main() {
    let options = AppConfig {
        foo: default(),
        bar: BarConfig {
            bar: 10.1,
            ..default()
        },
    };
}
    © 2010 The Rust Project Developers
Licensed under the Apache License, Version 2.0 or the MIT license, at your option.
    https://doc.rust-lang.org/std/default/fn.default.html