Yes. Use `dev-dependencies`. From the [Cargo docs][1]:

&gt; You can add a `[dev-dependencies]` section to your `Cargo.toml` whose format is equivalent to `[dependencies]`:
&gt; 
&gt; &lt;!-- language: toml --&gt;
&gt; 
&gt;     [dev-dependencies]
&gt;     tempdir = &quot;0.3&quot;
&gt; 
&gt; Dev-dependencies are not used when compiling a package for building,
&gt; but are used for compiling tests, examples, and benchmarks.

When possible, you should also use Cargo&#39;s [resolver version 2][2] to better handle complicated dev-dependency cases.

  [1]: https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#development-dependencies
  [2]: https://doc.rust-lang.org/cargo/reference/resolver.html#resolver-versions

I have the following code in `Python`:

    from selenium.webdriver import Firefox
    from contextlib import closing
    
    with closing(Firefox()) as browser:
      browser.get(url)

I would like to print the user-agent HTTP header and
possibly change it. Is it possible?



Change user-agent for Selenium web-driver

In Django, custom managers are a great way to organize reusable query logic. The [Django documentation on **Custom managers**][1] says:

&gt; There are two reasons you might want to customize a `Manager`: to add extra `Manager` methods, and/or to modify the initial `QuerySet` the `Manager` returns.

However, [it goes on to describe][2] how custom `QuerySet` classes can also be created, and that these can be made accessible directly from the data model as a manager using `QuerySet.as_manager()`:

&gt; The `Manager` instance created by `QuerySet.as_manager()` will be virtually identical to the `PersonManager` from the previous example.

It seems like there is a lot of flexibility in how one could organize their logic between custom `Manager` and/or custom `QuerySet` classes. What are the principles by which I should decide when to use one versus the other?


  [1]: https://docs.djangoproject.com/en/3.0/topics/db/managers/#custom-managers
  [2]: https://docs.djangoproject.com/en/3.0/topics/db/managers/#creating-a-manager-with-queryset-methods

When should I use a custom Manager versus a custom QuerySet in Django?

I have a Rust library that implements a lint plugin. I want to include `compiletest`, but not require it outside of testing. What is the correct way to specify that the dependency is for testing only?

How to define test-only dependencies?

<p>I have a Rust library that implements a lint plugin. I want to include <code>compiletest</code>, but not require it outside of testing. What is the correct way to specify that the dependency is for testing only?</p>


In Rust, when we want a struct to contain references, we typically define their lifetimes as such:

    struct Foo&lt;&#39;a&gt; {
    	x: &amp;&#39;a i32,
    	y: &amp;&#39;a i32,
    }

But it&#39;s also possible to define multiple lifetimes for different references in the same struct:

    struct Foo&lt;&#39;a, &#39;b&gt; {
    	x: &amp;&#39;a i32,
    	y: &amp;&#39;b i32,
    }

When is it ever useful to do this? Can someone provide some example code that doesn&#39;t compile when both lifetimes are `&#39;a` but does compile when the lifetimes are `&#39;a` and `&#39;b` (or vice versa)?

When is it useful to define multiple lifetimes in a struct?

I have a slice of `&amp;[u8]` and I&#39;d like to append it to a `Vec&lt;u8&gt;` with minimal copying. Here are two approaches that I know work:

    let s = [0u8, 1u8, 2u8];
    let mut v = Vec::new();
    v.extend(s.iter().map(|&amp;i| i));
    v.extend(s.to_vec().into_iter()); // allocates an extra copy of the slice

Is there a better way to do this in Rust stable? (`rustc 1.0.0-beta.2`)

What&#39;s the idiomatic way to append a slice to a vector?

Although vectors are best suited for procedural programming, I would like to use a `map` function on them. The following snippet works:

    fn map&lt;A, B&gt;(u: &amp;Vec&lt;A&gt;, f: &amp;Fn(&amp;A) -&gt; B) -&gt; Vec&lt;B&gt; {
        let mut res: Vec&lt;B&gt; = Vec::with_capacity(u.len());
        for x in u.iter() {
            res.push(f(x));
        }
        res
    }
    
    fn f(x: &amp;i32) -&gt; i32 {
        *x + 1
    }
    
    fn main() {
        let u = vec![1, 2, 3];
        let v = map(&amp;u, &amp;f);
        println!(&quot;{} {} {}&quot;, v[0], v[1], v[2]);
    }

Why isn&#39;t there any such function in the standard library? (and also in `std::collections::LinkedList`). Is there another way to deal with it?

Using map with Vectors

How do I concatenate the following combinations of types:

* `str` and `str`
* `String` and `str`
* `String` and `String`



How do I concatenate strings?

What are the **specific conditions** for a closure to implement the `Fn`, `FnMut` and `FnOnce` traits?

That is:

 + When does a closure *not* implement the `FnOnce` trait?
 + When does a closure *not* implement the `FnMut` trait?
 + When does a closure *not* implement the `Fn` trait?

For instance, mutating the state of the closure on it&#39;s body makes the compiler not implement `Fn` on it.


When does a closure implement Fn, FnMut and FnOnce?

I&#39;d like to update a package that I used `cargo install` to globally install packages, such as rustfmt or racer. I can&#39;t find a way to update an installed package without first deleting it (via `cargo uninstall`) and then running the install command again. Is there an update command?

Does cargo install have an equivalent update command?

I have a crate with both a binary and a library. The library is extremely light on dependencies, while the binary requires quite a bit more to, e.g., load files or do scoped parallel things.

Currently, I have my Cargo.toml set up like this:

    [dependencies.kdtree]
    path = &quot;../kdtree&quot;
    
    [dependencies]
    rand=&quot;0.3.0&quot;
    rustc-serialize = &quot;0.3&quot;
    csv = {git = &quot;https://github.com/BurntSushi/rust-csv.git&quot;}
    crossbeam = &quot;0.2&quot;
    num_cpus = &quot;0.2&quot;
    
    [lib]
    name = &quot;conformal&quot;
    path = &quot;src/lib.rs&quot;
    
    [[bin]]
    name = &quot;ucitest&quot;
    path = &quot;src/bin/main.rs&quot;

The only dependencies the library needs are the `kdtree` and `rand`. However, it seems like even if you only build the library, it goes and builds the binary-only dependencies anyway. I&#39;ve tried using `features` and other tricks like `[[bin].dependencies]` or `[ucitest-dependencies]` (or adding a `dependencies= []` line under `[[bin]]`) that I thought might make them only build for the binary, but I can&#39;t find a way.

These aren&#39;t enough dependencies to make this a problem, but it&#39;s bothering me. Is there a way to narrow down dependencies so they only build for specific binaries?

How can I specify binary-only dependencies?

I&#39;d like to make a project with a `daemon` and a `client`, connecting through a unix socket. 

A `client` and a `daemon` requires two binaries, so how do I tell `Cargo` to build two targets from two different sources?

To add a bit of fantasy, I&#39;d like to have a `library` for the main part of the `daemon`, and just have a binary to wrap around it and communicate through sockets.

So, we have this kind of tree architecture:

    ├── Cargo.toml
    ├── target
    |   └── debug
    |       ├── daemon
    │       └── client
    └── src
        ├── daemon
        │   ├── bin
        │   │   └── main.rs
        │   └── lib
        │       └── lib.rs
        └── client
            └── bin
                └── main.rs

I could make one executable which manages both concerns, but that&#39;s not what I want to do, unless it&#39;s very good practice.

How can I build multiple binaries with Cargo?

I seem to have diverging versions of `rustc` and `cargo` (I think), 

&lt;!-- language: none --&gt;

    $ rustc -V
    rustc 1.9.0 (e4e8b6668 2016-05-18)
    $ cargo -V
    cargo 0.10.0-nightly (10ddd7d 2016-04-08)

Is there a command akin to 

&lt;!-- language: none --&gt;

    pip install --upgrade pip 

for upgrading `cargo`? I.e. something like

&lt;!-- language: none --&gt;

    cargo install --upgrade cargo

Is there a command to update Cargo to the latest official release?

The following command

    $ cargo build

produces a **non-optimized** build **with** debugging information. On the contrary,

    $ cargo build --release

produces an **optimized** build **without** debugging information.

Is there a way of producing an **optimized** build **with** debugging information? I need this to get meaningful profiling information.


Content Type	Original Author	Original Content on Stackoverflow
Question	llogiq	View Question on Stackoverflow
Solution 1 - Rust	Shepmaster	View Answer on Stackoverflow

How to define test-only dependencies?

Rust Problem Overview

Rust Solutions

Solution 1 - Rust

When should I use a custom Manager versus a custom QuerySet in Django?

Change user-agent for Selenium web-driver

Attributions