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我可能遗漏了一些非常基本的东西——我是 Rust 的新手。我正在尝试将petgraph::dot::Dot表示写入文件。

以下小代码示例无法编译:

use petgraph::Graph;
use petgraph::dot::{Dot, Config};
use std::fs::File;
use std::io::Write;


fn main() {
    println!("hello graph!");
    let mut graph = Graph::<_, ()>::new();
    graph.add_node("A");
    graph.add_node("B");
    graph.add_node("C");
    graph.add_node("D");
    graph.extend_with_edges(&[
        (0, 1), (0, 2), (0, 3),
        (1, 2), (1, 3),
        (2, 3),
    ]);

    println!("{:?}", Dot::with_config(&graph, &[Config::EdgeNoLabel]));
    let mut f = File::create("example1.dot").unwrap();
    let output = format!("{}", Dot::with_config(&graph, &[Config::EdgeNoLabel]));
    f.write_all(&output.as_bytes());
}

这是编译器错误输出:

error[E0277]: `()` doesn't implement `std::fmt::Display`
  --> examples/graphviz.rs:21:32
   |
21 |     let output = format!("{}", Dot::with_config(&graph, &[Config::EdgeNoLabel]));
   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `()` cannot be formatted with the default formatter
   |
   = help: the trait `std::fmt::Display` is not implemented for `()`
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
   = note: required because of the requirements on the impl of `std::fmt::Display` for `petgraph::dot::Dot<'_, &petgraph::graph_impl::Graph<&str, ()>>`
   = note: required by `std::fmt::Display::fmt`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.

petgraph 文档指出Dot 实现了 Display 特征,我的代码基于trait.Display 文档中的示例代码

我可以通过将格式字符串更改为来使代码工作,{:?}但我认为这只是为了调试。有没有更好的方法来编写代码来完成同样的事情?

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1 回答 1

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DotDisplay仅当边缘和节点权重都实现时才实现Display

由于您的边是(),因此您无法显示此图。

例如,将图形声明更改为使用i32边权重:

    let mut graph = Graph::<_, i32>::new();

导致程序编译没有错误。

于 2019-08-17T22:29:19.377 回答