Cannot implement quickchecks Arbitrary for my own type - "source trait is private"

Question

I am using quickcheck to validate some properties of my code. At one point, I need an ASCII byte, so I tried to write an implementation of Arbitrary like this:

cat test.sh | awk '{print $1}'

This fails with the error:

extern crate quickcheck;

use quickcheck::{quickcheck,Arbitrary,Gen};

#[derive(Debug,Copy,Clone)]
struct AsciiChar(u8);

impl Arbitrary for AsciiChar {
    fn arbitrary<G>(g: &mut G) -> AsciiChar
        where G: Gen
    {
        let a: u8 = g.gen_range(0, 128);
        AsciiChar(a)
    }
}

#[test]
fn it_works() {}

Some searching led me to various bug reports (1, 2, 3, 4) that all seem to suggest I need to src/lib.rs:12:21: 12:40 error: source trait is private src/lib.rs:12 let a: u8 = g.gen_range(0, 128); ^~~~~~~~~~~~~~~~~~~ the supertrait of Gen, which is rand::Rng. I updated my crates and use statements to

use

But I continue to get the same error.

I've tried with

• extern crate quickcheck; extern crate rand; use rand::Rng; use quickcheck::{quickcheck,Arbitrary,Gen};
• rustc version 1.1.0-dev (b402c43f0 2015-05-07) (built 2015-05-07)

I'm also using rustc 1.1.0-dev (3ca008dcf 2015-05-12) (built 2015-05-12)

Answer 1

啊，这是一个棘手的问题。为了进行测试，我添加了这个hack：

impl Arbitrary for AsciiChar {
    fn arbitrary<G>(g: &mut G) -> AsciiChar
        where G: Gen
    {
        let a: u8 = Arbitrary::arbitrary(g);
        AsciiChar(a % 128)
    }
}

编译之后，我收到了这个错误：

src/lib.rs:419:5: 419:23 error: use of unstable library feature 'rand': use `rand` from crates.io
src/lib.rs:419     extern crate rand;
                   ^~~~~~~~~~~~~~~~~~
src/lib.rs:419:5: 419:23 help: add #![feature(rand)] to the crate attributes to enable

我的问题是我忘了将rand添加到Cargo.toml 。我想我会疯狂地通过quickcheck获得同样的版本。

最终的问题是，我没有实际上use正确的Rng版本，Gen是其中的一个子版本。非常混乱！

将rand添加到Cargo.toml后，我又回来了。

Answer 2

这很奇怪。我可以重现您的初始错误，但您建议的修复程序适用于我：

extern crate quickcheck;
extern crate rand;

use quickcheck::{Arbitrary,Gen};
use rand::Rng;

#[derive(Debug,Copy,Clone)]
struct AsciiChar(u8);

impl Arbitrary for AsciiChar {
    fn arbitrary<G>(g: &mut G) -> AsciiChar
        where G: Gen
    {
        let a: u8 = g.gen_range(0, 128);
        AsciiChar(a)
    }
}

#[test]
fn it_works() {}

在beta5和2015-05-12夜间作品上运行cargo test。