Rust map option to result
Rust map option to result. flat_map(|e| e). and_then() and . Apr 23, 2023 · Using filter_map(Result::transpose) works nicely in this particular case because it is filtering Result<Option<T>, E>, and the transformation to Option<Result<T, E>> will ensure that all None values are simply ignored while simultaneously unwrapping the Option. ok_or(MissingFieldError). Dec 5, 2020 · I would like to write some code in a "functional programming" style. checked_add(c)). flatten(). – Apr 1, 2022 · Using map. These functions have slightly different patterns, but you’ll find that we already have a generalization for this, albeit a bit more restrictive than the inherent functions. Both Result and Option offer a transpose method to do Now available on Stack Overflow for Teams! AI features where you work: search, IDE, and chat. This function can be used to compose the results of two functions. Does Option have a nice method for this? Apr 1, 2022 · Is there a simple way to convert an Option<Result<T, E>> to an Option<T>, returning Err in case of error? Mar 23, 2022 · It's also helpful to explore the rustdocs on Option and Result to see if you can "fit the puzzle pieces" together on how to get between them. Here is an example: My first thought is to map the Option, but I can't use try! from inside of the closure. map_or takes a value, this means the "or" has to be evaluated before the method is even called, that is in a. For example, you have an Option<String> and you want to parse it as an integer. §Examples. let some_number = Some(9); // Let's do some consecutive calculations with our number. Transposition is the operation to swap a Result and Option in a nested type. Rust provides two primary methods on Option for converting to a Result: ok_or and ok_or_else. Rust 1. map(unmarshall_child). ok_or. Learn more Explore Teams Mar 16, 2022 · I usually encountered scenarios where I need to chain Option or Result locally (the function return value is not an Option or Result). ok_or("no item1")?; let item2 = section. collect() These methods also work for Option, which also implements IntoIterator. Hot Network Questions 2 identical red balls and 3 identical black balls in 5 different boxes, each box contain at most 2 Feb 25, 2016 · 注意： rusti で型を見ると core ライブラリの Option<T> 型が優先されてしまいます。 通常の Rust プログラムでは core ライブラリを use 指定してないので、core ではなく、std ライブラリの std::option::Option<T> 型になります。 Oct 15, 2024 · The iterator will either produce a single value (when the Option is Some), or produce no values (when the Option is None). opt. 70. fn example<T, E>(val: The map operation is a useful tool when working with arrays and vectors, but it can also be used to deal with Option values in a functional way. map(|s| s. I don't see any useful functions in the documentation for Result either unfortunately. checked_add(d)) { // do something with sum } else { // other logic } I used to Jul 2, 2015 · Rust - evaluate result in Option map closure. map_or(None, _) does Nov 3, 2017 · When working with optional value via . Let say we want to perform checked sum on four integers, the usual way I write this procedure is if let Some(sum) = a. Iterators over Option<T> come in three types: into_iter consumes the Option and produces the contained value Jan 22, 2020 · I know we can use collect to move a Result from inner to outer, like: fn produce_result(my_struct: &MyStruct) -> Result<MyStruct, Error>; let my_results: Vec<MyStruct> = vec![] Sep 20, 2022 · It seems to me here they are all kinda "lazy". Let‘s explore them in more detail. Furthermore, I wan Jan 5, 2023 · When writing Rust code, it’s common to have an Option value that you want to map through some fallible operation. For example, into_iter acts like once(v) if the Option is Some(v), and like empty() if the Option is None. The ok_or method takes a single parameter – the error value to use in the Result if the Option is None: fn option_to_result(opt: Option<i32>) -> Result<i32, &‘static str> { Oct 15, 2024 · Maps an Option<T> to Option<U> by applying a function to a contained value (if Some) or returns None (if None). The Result type. 💭 In the previous sections, we have discussed about the basics of enums, generics and Result & Option types. map(str::parse::<MyType>) A variant of that is: json_value["field"]. Types added for clarity: For symmetry's sake, there's also Option::ok_or and Option::ok_or_else to go from an Option to a Result. Jan 12, 2021 · One options that comes to mind is: json_value["field"]. Feb 1, 2024 · Rust skips using both, especially to prevent issues like null pointer exceptions, sensitive data leakages through exceptions, etc. Using into_iter with Option. map_or(b, fn) Rust has to first fully evaluate a and b before it can call map_or. So my question is actually how can I easily parse an optional value by avoiding if/else conditions in Rust? 0 写在前面本文主要介绍 rust 编程语言中 Option 和 Result 枚举的使用方法。适合已经了解 rust 编程语言的程序员阅读。如果想更系统的了解 rust 中错误处理的相关内容，请先移步： Rust语言圣经(Rust Course)1 Op… Jan 26, 2022 · As Lukas suggested, the map_or method can also be used. Feb 21, 2022 · In the Rust By Example book show us a way to handle errors in the map method of Iterator: let strings = vec!["93", "tofu", "18";]; let numbers: Result<Vec< So what bothers me is that I can perfectly fine map the inner value of Option<T> manually, using if let syntax and return early from the method but cannot just . Calculates the length of an Option<String> as an Option<usize>, consuming the original: The crucial difference is that map returns an Option<U> and map_or instead a plain unwrapped U! It can do that because there's always a U available: either the result of applying f or the default value. collect() Iterator::flat_map: vec. . flip_inside_out()?. As you know, Jun 7, 2018 · It seems like you want Option::and_then:. Since Result implements IntoIterator, you can convert your Vec into an iterator (which will be an iterator of iterators) and then flatten it: Iterator::flatten: vec. Converts from Option<T> to Option<&T>. and_then(|v| v. fn main() { // We start with an Option value (Option<i32> in this case). and_then(str::parse::<MyType>) Converting Option to Result. Using expect, unwrap, match, and if let. ok_or("mising field"). Examples. Convert an Option<String> into an Option<usize>, preserving the original. 70+ The is_some_and method has been stabilized in Rust 1. checked_add(b). ok_or("no item2")?; // whatever processing Use Result::ok. map(f). However, I start with an Iterator of Results and I only want to apply the function to the Ok items. In your example there is some logic to the filter so I don't think it simplifies things. Nov 3, 2017 · When working with optional value via . as_str(). Jul 10, 2021 · Both Result and Option are container types that wrap a value of type T. Note that arguments passed to map_or are eagerly evaluated, so if performance is critical, you might want to consider map_or_else as an alternative. pub fn and_then<U, F>(self, f: F) -> Option<U> where F: FnOnce(T) -> Option<U> Examples: fn sq(x: u32) -> Option<u32> { Some Of note, Option::map is the equivalent of Result::map, while Option::and_then is the equivalent of Result::and_then. map() I often end up with Option<Result<T>>, but I want to check the result and end up with Option<T> or return from a function early. map() the inner value of Option<T>. Does Option have a nice method for this? So far the shortest I know is: let optional = if let Some(tmp) = optional { Some(tmp?) } else { None }; but I'd prefer something shorter like optional. The map method takes the self argument by value, consuming the original, so this technique uses as_ref to first take an Option to a reference to the value inside the original. The ok_or and ok_or_else methods convert Options to Results, and the ? operator automates the boilerplate associated with early Err returns. You could do something like this: fn parse_maybe_int (s: Option < String >) -> Option < Result < i32, ParseIntError>> { s. If you'd like to ignore failures, use Iterator::flat_map. transpose(). unwrap_or(d)! So U in this case is Result<Option<i32>, _>, which is why opt. You could do something like: fn new() -> Result<Boo, String> { let item1 = section. The match statement looks unnecessary, but I can't figure out how to simplify it. In your case, you have an iterator. But that type T can just as well be a Result and an Option too. This is very much a functional solution to the problem. Instead, Rust provides two special generic enums;Option and Result to deal with above cases. Using ok_or. So, for example, a Result<Option<T>> becomes a Option<Result<T>> or vice versa. Print the numbers on each line of a string multiplied by two. get("item2"). The ideas behind Option and Result are not new to Rust. What exactly does it mean to be eager/lazy when it comes to Result::map_or_else, Result::map_or, and alike in Option?. parse::< i32 >()) } Apr 2, 2016 · filter_map can be used to reduce simple cases of mapping then filtering. Oct 15, 2024 · Maps a Result<T, E> to Result<U, E> by applying a function to a contained Ok value, leaving an Err value untouched. get("item1"). In your additional example, probably something like opt. into_iter(). map_or(d, f) is equivalent to opt. khlzw hxajbsyg yacm gwzoh mvh wlyi ogjn jcbvd zro rssjj