I want one argument to imply another, though they don't take explicit values. --simple-anime or --complex-anime should imply --anime. The API that should work is default_value_ifs, saying that if either of the former is present, --anime will also be true. The problem is that that option turns on takes_value, and if I turn that off, the implication doesn't happen.
Simple example: --dog implies --mammal. Neither one should require a value--it is true if the argument is present.
use clap::Parser;
fn main() {
let args = Args::parse_from(["prog-name", "--dog"]);
assert_eq!(args.dog, true);
assert_eq!(args.mammal, true);
dbg!(&args);
let args = Args::try_parse_from(["prog-name", "--mammal"]);
dbg!(&args);
assert!(matches!(args, Ok(_)));
}
#[derive(Parser, Debug)]
#[clap()]
struct Args {
//#[clap(long, default_value_if("dog", None, Some("true")), takes_value(false))]
#[clap(long, default_value_if("dog", None, Some("true")))]
mammal: bool,
#[clap(long)]
dog: bool,
}
Try it in rust playground: https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=4855a88381f65cef8d07f7eab4d41e78
Instead of takes_value(false) use min_values(0) (playground):
#[clap(long, default_value_if("dog", None, Some("true")), min_values(0))]
mammal: bool,
It looks like the default value implementation uses the same code as the values, so if you disable one you disable the other.
Related
I'm implementing a tokio/axum HTTP server. In the function where I run the server, I configure routing, add shared application services and add tracing layer.
My tracing configuration looks like this:
let tracing_layer = TraceLayer::new_for_http()
.make_span_with(|_request: &Request<Body>| {
let request_id = Uuid::new_v4().to_string();
tracing::info_span!("http-request", %request_id)
})
.on_request(|request: &Request<Body>, _span: &Span| {
tracing::info!("request: {} {}", request.method(), request.uri().path())
})
.on_response(
|response: &Response<BoxBody>, latency: Duration, _span: &Span| {
tracing::info!("response: {} {:?}", response.status(), latency)
},
)
.on_failure(
|error: ServerErrorsFailureClass, _latency: Duration, _span: &Span| {
tracing::error!("error: {}", error)
},
);
let app = Router::new()
// routes
.layer(tracing_layer)
// other layers
...
Trying to organize the code a bit I move the tracing layer configuration to a separate function. The trick is to provide a compiling return type for this function.
The first approach was to move the code as is and let an IDE generate the return type:
TraceLayer<SharedClassifier<ServerErrorsAsFailures>, fn(&Request<Body>) -> Span, fn(&Request<Body>, &Span), fn(&Response<BoxBody>, Duration, &Span), DefaultOnBodyChunk, DefaultOnEos, fn(ServerErrorsFailureClass, Duration, &Span)>
Which is completely unreadable, but the worst is it does not compile: "expected fn pointer, found closure"
In the second approach I changed fn into impl Fn that would mean a closure type. Again, I get an error that my closures are not Clone.
Third, I try to extract closures into separate functions. But then I get "expected fn pointer, found fn item".
What can I do 1) to make it compile and 2) to make it more readable?
Speaking from experience, breaking up the code like that is very hard due to all the generics. I would instead recommend functions that accept and return axum::Routers. That way you bypass all the generics:
fn add_middleware(router: Router) -> Router {
router.layer(
TraceLayer::new_for_http().make_span_with(...)
)
}
I'm convinced there is a way to handle this 'cleanly', I am just not quite figuring it out.
use git2::Repository;
// Prints out the current branch and sha if it exists.
fn report_repo() -> () {
Repository::open(".")
.ok()
.and_then(branch_and_sha)
.and_then(|branch_sha| => { // Fails here with E0061
let (branch, sha) = branch_sha;
println!("Branch={} sha={}", branch, sha);
None
});
}
fn branch_and_sha(repo: Repository) -> Option<(String, String)> {
match repo.head().ok() {
Some(reference) => {
match (reference.name(), reference.target()){
(Some(branch), Some(sha)) => Some((branch.to_string(), sha.to_string())),
_ => None
}
},
None => None
}
}
The error that arises is E0061, and I think it's because the 'value' in the Option returned from branch_and_sha() is a tuple. branch_and_sha() effectively says, "If there is a repository, get it's reference, and if that exists, if it has both a name (branch) and target (sha), return an Option<(String, String)> with that info - otherwise return None. And the reporting function wants to do something if all of the Repository, branch and sha can be found - and nothing otherwise. (It shouldn't error or panic.)
To some degree this is contrived - it's an example of an optimistic reporting function similar to several I'd like to write. I'm looking for a clean, idiomatic way to do it. The key thrust is 'several depths and several branches could return None which should cause a no-op, and otherwise make specific (leaf) info available.' The specific error is how I should be handling the and_then function, which is surprisingly difficult to find similar problems about.
First off, you have a minor typo. Closures in Rust don't use =>. So your closure should look more like
.and_then(|branch_sha| { // Note: No => here
let (branch, sha) = branch_sha;
println!("Branch={} sha={}", branch, sha);
None
});
Then the error we get is
--> so_cleanly.rs:15:10
|
15 | .and_then(|branch_sha| {
| ^^^^^^^^ cannot infer type for type parameter `U` declared on the associated function `and_then`
|
and_then is declared with two generic arguments: U and F (technically, there's also T, but that's determined by the type of the receiver self, so we won't worry about it). Now, F is the type of the closure and is always determined by the argument. On the other hand, U is the return type of the closure.
The closure must return an Option<U>. Rust needs to look at the closure and determine what its return type is. What does the closure return? It returns None, and None can be Option<U> for any U in existence. Rust doesn't know which one to use. We need to tell it. We could do that on the line we return None from
None as Option<()>
or in the and_then call itself.
.and_then::<(), _>(|branch_sha| { ... })
However, the compiler is making a very valid point. and_then and company produce a result of type Option, which you're ignoring. You're writing a piece of code which has side effects and doesn't produce a value, which is sensible, but you're using a functional interface intended for returning values. It can be done, but it's probably not idiomatic. I had to look at your code a few times before realizing that the () return value was not a typo.
One option is to return Option<()> from your report_repo. The () on the inside indicates that we don't care about anything except the side effects, and the Option lets the caller of report_repo handle (or ignore) any errors that occur during the process, whereas your current function simply suppresses all errors unconditionally.
fn report_repo() -> Option<()> {
Repository::open(".")
.ok()
.and_then(branch_and_sha)
.map(|branch_sha| {
let (branch, sha) = branch_sha;
println!("Branch={} sha={}", branch, sha);
// Implicit return of () here, which we could do explicitly if we wanted
})
}
I've made several subtle changes here. The return type is Option<()> now. In accordance with that, there's no semicolon at the end of the line inside the function (we're returning that value). Finally, the last and_then is a map, since the final step can't fail and simply does some work on Some.
That's an improvement, but it's probably still not how I'd write this function.
Instead, if you're performing code for side effects, consider using the ? operator, which does and_then and map shenanigans but keeps the control flow relatively linear. and_then and its friends are great for constructing values, but the point of your function is that it should read like a sequence of instructions, not a constructor for a value. This is how I would write that function.
fn report_repo() -> Option<()> {
let repo = Repository::open(".").ok()?;
let (branch, sha) = branch_and_sha(repo)?;
println!("Branch={} sha={}", branch, sha);
Some(())
}
Each line that ends in a ? effectively says "If this thing is None, return None now. Otherwise, keep going." But a cursory glance of the code reads "open the repo, branch and sha, and then print", which is exactly what you want people to see at a glance.
If we wanted to be really proper about this, we should probably return Result<(), Error>, where Error is some more detailed error type, but that's overkill for this simple example snippet.
You can chose an if let style too, you do not need the option value so just stop using them at some point it feels more comfortable:
fn report_repo() {
if let Some((branch, sha)) = Repository::open(".").ok().and_then(branch_and_sha) {
println!("Branch={} sha={}", branch, sha);
}
}
I'm learning how to use neon, but I don't understand a thing. If I try to execute this code:
#[macro_use]
extern crate neon;
use neon::vm::{Call, JsResult};
use neon::mem::Handle;
use neon::js::{JsInteger, JsNumber, JsString, JsObject, JsArray, JsValue, Object, Key};
use neon::js::error::{JsError, Kind};
fn test(call: Call) -> JsResult<JsArray> {
let scope = call.scope;
let js_arr: Handle<JsArray> = try!(try!(call.arguments.require(scope, 1)).check::<JsArray>());
js_arr.set(0, JsNumber::new(scope, 1000));
Ok(js_arr)
}
register_module!(m, {
m.export("test", test)
});
I get this error when I call js_arr.set: This function takes 3 parameters but 2 were supplied.
I don't understand why since it's a JsArray. Even Racer tells me that the set method takes 2 parameters. No matter what, js_arr.set takes 3 parameters in this order: &mut bool, neon::macro_internal::runtime::raw::Local and neon::macro_internal::runtime::raw::Local.
What's happening? I can't understand how JsArray works.
As paulsevere says on a GitHub issue for Neon, import neon::js::Object. In addition, do not import Key, which also provides a set method:
#[macro_use]
extern crate neon;
use neon::vm::{Call, JsResult};
use neon::js::{Object, JsArray, JsInteger, JsObject, JsNumber};
fn make_an_array(call: Call) -> JsResult<JsArray> {
let scope = call.scope; // the current scope for rooting handles
let array = JsArray::new(scope, 3);
array.set(0, JsInteger::new(scope, 9000))?;
array.set(1, JsObject::new(scope))?;
array.set(2, JsNumber::new(scope, 3.14159))?;
Ok(array)
}
register_module!(m, {
m.export("main", make_an_array)
});
This creates a brand new array. If you'd like to accept an array as the first argument to your function and then modify it, this works:
#[macro_use]
extern crate neon;
use neon::vm::{Call, JsResult};
use neon::js::{Object, JsArray, JsInteger, JsUndefined};
use neon::mem::Handle;
fn hello(call: Call) -> JsResult<JsUndefined> {
let scope = call.scope;
let js_arr: Handle<JsArray> = call.arguments.require(scope, 0)?.check::<JsArray>()?;
js_arr.set(0, JsInteger::new(scope, 1000))?;
Ok(JsUndefined::new())
}
register_module!(m, {
m.export("hello", hello)
});
let js_arr: Handle<JsArray> makes it clear that js_arr is a Handle<JsArray> and Handle<T> has this method:
unsafe fn set(self, out: &mut bool, obj: Local, val: Local) -> bool
I'd guess that you're accidentally trying to call Handle::set (which is unsafe and takes three non-self arguments) rather than JsArray::set (which is safe and takes two non-self arguments).
If that's the case, you need to force a deref_mut to occur. (_mut because JsArray::set takes &mut self.)
I haven't run into this sort of naming collision before, so I can't be certain whether the auto-deref is smart enough, but something like this may work:
(&mut js_arr).set(0, JsNumber::new(scope, 1000));
Failing that, two other things to try are:
JsArray::set(&mut js_arr, 0, JsNumber::new(scope, 1000));
(If the former example fails because it's too much like C++-style method overloading. This is known as Fully Qualified Syntax and is normally used to disambiguate when an object implements two traits which provide methods of the same name.)
Call js_arr.deref_mut() directly to get a mutable reference to the underlying JsArray, then call set on that.
Lets say I want to write a little client for an HTTP API. It has a resource that returns a list of cars:
GET /cars
It also accepts the two optional query parameters color and manufacturer, so I could query specific cars like:
GET /cars?color=black
GET /cars?manufacturer=BMW
GET /cars?color=green&manufacturer=VW
How would I expose these resources properly in Rust? Since Rust doesn't support overloading, defining multiple functions seems to be the usual approach, like:
fn get_cars() -> Cars
fn get_cars_by_color(color: Color) -> Cars
fn get_cars_by_manufacturer(manufacturer: Manufacturer) -> Cars
fn get_cars_by_manufacturer_and_color(manufacturer: Manufacturer, color: Color) -> Cars
But this will obviously not scale when you have more than a few parameters.
Another way would be to use a struct:
struct Parameters {
color: Option<Color>,
manufacturer: Option<Manufacturer>
}
fn get_cars(params: Parameters) -> Cars
This has the same scaling issue, every struct field must be set on creation (even if its value is just None).
I guess I could just accept a HashMap<String, String>, but that doesn't sound very good either.
So my question is, what is the proper/best way to do this in Rust?
You could use the Builder pattern, as mentioned here. For your particular API, it could look like this:
Cars::new_get()
.by_color("black")
.by_manufacturer("BMW")
.exec();
I would like to point out that no matter the solution, if you wish for a compile-time checked solution the "url parsing -> compile-time checkable" translation is necessarily hard-wired. You can generate that with an external script, with macros, etc... but in any case for the compiler to check it, it must exist at compile-time. There just is no short-cut.
Therefore, no matter which API you go for, at some point you will have something akin to:
fn parse_url(url: &str) -> Parameters {
let mut p: Parameters = { None, None };
if let Some(manufacturer) = extract("manufacturer", url) {
p.manufacturer = Some(Manufacturer::new(manufacturer));
}
if let Some(color) = extract("color", url) {
p.color = Some(Color::new(color));
}
p
}
And although you can try and sugarcoat it, the fundamentals won't change.
I'm trying to declare a map in a separate file, and then access it from my main function.
I want Rust's equivalent (or whatever comes closest) to this C++ map:
static const std::map<std::string, std::vector<std::string>> table = {
{ "a", { "foo" } },
{ "e", { "bar", "baz" } }
};
This is my attempt in Rust.
table.rs
use std::container::Map;
pub static table: &'static Map<~str, ~[~str]> = (~[
(~"a", ~[~"foo"]),
(~"e", ~[~"bar", ~"baz"])
]).move_iter().collect();
main.rs
mod table;
fn main() {
println(fmt!("%?", table::table));
}
The above gives two compiler errors in table.rs, saying "constant contains unimplemented expression type".
I also have the feeling that the map declaration is less than optimal for the purpose.
Finally, I'm using Rust 0.8.
As Chris Morgan noted, rust doesn't allow you to run user code in order to initialize global variables before main is entered, unlike C++. So you are mostly limited to primitive types that you can initialize with literal expressions. This is, afaik, part of the design and unlikely to change, even though the particular error message is probably not final.
Depending on your use case, you might want to change your code so you're manually passing your map as an argument to all the functions that will want to use it (ugh!), use task-local storage to initialize a tls slot with your map early on and then refer to it later in the same task (ugh?), or use unsafe code and a static mut variable to do much the same with your map wrapped in an Option maybe so it can start its life as None (ugh!).