如何在Rust 1.0中获得随机数? [英] How can I get a random number in Rust 1.0?
问题描述
我尝试过
use std::rand::{task_rng, Rng};
fn main() {
// a number from [-40.0, 13000.0)
let num: f64 = task_rng().gen_range(-40.0, 1.3e4);
println!("{}", num);
}
但这给了
error[E0432]: unresolved import `std::rand::task_rng`
--> rand.rs:1:17
|
1 | use std::rand::{task_rng, Rng};
| ^^^^^^^^ no `task_rng` in `rand`
error[E0432]: unresolved import `std::rand::Rng`
--> rand.rs:1:27
|
1 | use std::rand::{task_rng, Rng};
| ^^^ no `Rng` in `rand`
error[E0603]: module `rand` is private
--> rand.rs:1:17
|
1 | use std::rand::{task_rng, Rng};
| ^^^^^^^^
error[E0603]: module `rand` is private
--> rand.rs:1:27
|
1 | use std::rand::{task_rng, Rng};
| ^^^
我尝试了
extern crate rand;
use rand::Rng;
fn main() {
let mut rng = rand::thread_rng();
if rng.gen() {
// random bool
println!("i32: {}, u32: {}", rng.gen::<i32>(), rng.gen::<u32>())
}
let tuple = rand::random::<(f64, char)>();
println!("{:?}", tuple)
}
得到
error[E0425]: cannot find function `thread_rng` in module `rand`
--> rand.rs:5:29
|
5 | let mut rng = rand::thread_rng();
| ^^^^^^^^^^ not found in `rand`
|
help: possible candidate is found in another module, you can import it into scope
| use std::__rand::thread_rng;
error[E0425]: cannot find function `random` in module `rand`
--> rand.rs:10:27
|
10 | let tuple = rand::random::<(f64, char)>();
| ^^^^^^ not found in `rand`
error: use of unstable library feature 'rand': use `rand` from crates.io (see issue #27703)
--> rand.rs:1:5
|
1 | extern crate rand;
| ^^^^^^^^^^^^^^^^^^
error: use of unstable library feature 'rand': use `rand` from crates.io (see issue #27703)
--> rand.rs:2:9
|
2 | use rand::Rng;
| ^^^^^^^^^
过去， 然后您的示例代码起作用: 输出:
为什么从stdlib中删除了这些有用的功能? Rust的理念是将尽可能多的箱子放置在板条箱中，而不是放在标准库中.这样一来，每段代码都可以以与标准库不同的速率增长和发展，并且还可以停止使用而无需强制对其进行永久维护. 一个常见的示例是序列Python中的HTTP库.有多个软件包都以不同的方式执行相同的操作，并且Python维护人员必须保留全部 以便提供向后兼容性.rand板条箱是标准库的一部分，但很久以来一直是use rand::Rng; // 0.7.2
fn main() {
let mut rng = rand::thread_rng();
if rng.gen() { // random bool
println!("i32: {}, u32: {}", rng.gen::<i32>(), rng.gen::<u32>())
}
let tuple = rand::random::<(f64, char)>();
println!("{:?}", tuple)
}
$ cargo run
Running `target/debug/so`
i32: 1819776837, u32: 3293137459
(0.6052759716514547, '\u{69a69}')
$ cargo run
Running `target/debug/so`
(0.23882541338214436, '\u{10deee}')
I tried
use std::rand::{task_rng, Rng};
fn main() {
// a number from [-40.0, 13000.0)
let num: f64 = task_rng().gen_range(-40.0, 1.3e4);
println!("{}", num);
}
but this gives
error[E0432]: unresolved import `std::rand::task_rng`
--> rand.rs:1:17
|
1 | use std::rand::{task_rng, Rng};
| ^^^^^^^^ no `task_rng` in `rand`
error[E0432]: unresolved import `std::rand::Rng`
--> rand.rs:1:27
|
1 | use std::rand::{task_rng, Rng};
| ^^^ no `Rng` in `rand`
error[E0603]: module `rand` is private
--> rand.rs:1:17
|
1 | use std::rand::{task_rng, Rng};
| ^^^^^^^^
error[E0603]: module `rand` is private
--> rand.rs:1:27
|
1 | use std::rand::{task_rng, Rng};
| ^^^
and I tried
extern crate rand;
use rand::Rng;
fn main() {
let mut rng = rand::thread_rng();
if rng.gen() {
// random bool
println!("i32: {}, u32: {}", rng.gen::<i32>(), rng.gen::<u32>())
}
let tuple = rand::random::<(f64, char)>();
println!("{:?}", tuple)
}
and got
error[E0425]: cannot find function `thread_rng` in module `rand`
--> rand.rs:5:29
|
5 | let mut rng = rand::thread_rng();
| ^^^^^^^^^^ not found in `rand`
|
help: possible candidate is found in another module, you can import it into scope
| use std::__rand::thread_rng;
error[E0425]: cannot find function `random` in module `rand`
--> rand.rs:10:27
|
10 | let tuple = rand::random::<(f64, char)>();
| ^^^^^^ not found in `rand`
error: use of unstable library feature 'rand': use `rand` from crates.io (see issue #27703)
--> rand.rs:1:5
|
1 | extern crate rand;
| ^^^^^^^^^^^^^^^^^^
error: use of unstable library feature 'rand': use `rand` from crates.io (see issue #27703)
--> rand.rs:2:9
|
2 | use rand::Rng;
| ^^^^^^^^^
In the far past, the rand crate was part of the standard library but has long since been extracted to a crate. This crate should be the one you use:
Specify a Cargo.toml:
[package]
name = "stackoverflow"
version = "0.0.1"
authors = ["A. Developer <developer@example.com>"]
[dependencies]
rand = "0.7.0" # Or a newer version
Then your example code works:
use rand::Rng; // 0.7.2
fn main() {
let mut rng = rand::thread_rng();
if rng.gen() { // random bool
println!("i32: {}, u32: {}", rng.gen::<i32>(), rng.gen::<u32>())
}
let tuple = rand::random::<(f64, char)>();
println!("{:?}", tuple)
}
With the output:
$ cargo run
Running `target/debug/so`
i32: 1819776837, u32: 3293137459
(0.6052759716514547, '\u{69a69}')
$ cargo run
Running `target/debug/so`
(0.23882541338214436, '\u{10deee}')
Why were these useful functions removed from stdlib?
Rust has a philosophy of placing as much as possible into crates instead of the standard library. This allows each piece of code to grow and evolve at a different rate than the standard library and also allows the code to stop being used without forcing it to be maintained forever.
A common example is the sequence of HTTP libraries in Python. There are multiple packages that all do the same thing in different ways and the Python maintainers have to keep all of them to provide backwards compatibility.
Crates allow this particular outcome to be avoided. If a crate truly stabilizes for a long time, I'm sure it could be re-added to the standard library.
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