I have sketched out an example problem in the Rust playground. For reference, I will provide the full code at the end of this question. I have attempted to write the following function. fn get_longest_time_window(&self) -> Option<u64> { let lambda = |lhs: &Element, rhs: &Element| -> &Element { return if lhs.time_window >= rhs.time_window { lhs… Read More How to express lifetime constraints for closures which take and return references?

Suppose that I want to take a function that operates on two elements of a collection and turn it into a function that operates on two collections elementwise. For example, I want to turn a function adding two numbers together into a function that takes two collections of numbers and adds the numbers up elementwise.… Read More How to "vectorize" a function in Rust

I have Option<impl Fn(i64) -> i64> as an argument to a function apply() and I want to pass None value. apply(None). How do I write the apply(None) function call correctly so it compiles? fn main(){ let a = apply(Some(|i| i + 1)); let b = apply(None); let b2 = apply(None::<dyn Fn(i64) -> i64>); println!("a: {0};… Read More Rust empty explicit generic argument for Option<impl Fn(i64)>

How do to put two closures with the same definition into a Vec? Here is a minimal reproducible example: fn main() { let mut vec = Vec::new(); vec.push(Box::new(|| println!("test"))); vec.push(Box::new(|| println!("test2"))); vec.iter().for_each(|f| (f)()); } Which failed on compiling with following error: error[E0308]: mismatched types –> src/main.rs:4:23 | 3 | vec.push(Box::new(|| println!("test"))); | — the expected… Read More Rust no two closures, even if identical, have the same type

fn main() { let foo = 5; std::thread::spawn(|| { // closure may outlive the current function, but it borrows `foo`, which is owned by the current function println!("{}", foo); }) .join() .unwrap(); } Moving the value is not an option since it have to make multiple threads The situation in my code is a bit… Read More Closure might outlive current function even though it is joined

I have simple hashmap and want to manipulate it but IDE does not recognize the methods. Completely new to Groovy so not sure what is wrong. def percentages = [ "x1" : "20%", "x2" : "30%", "x3" : "0.4", "x4" : "50%", "x5" : "0.6"] percentages.each { val -> if(val[2].endsWith("%")) { val[2].deleteCharAt(val.length()-1) println val }… Read More Why I cannot use string methods inside groovy closure? – no candidate for method call

I’m trying to reproduce an error I’m having on my small app in Rust. I’m trying to use async closure as lambda functions (very tipical in other languages). But I just found out that this is a bit difficult in Rust: REPL: https://www.rustexplorer.com/b/bcwggm. Error: error: lifetime may not live long enough –> src/main.rs:55:9 | 54… Read More Using async closure as lambda functions is a bit hard

I want to retrieve the values of a and b from p in the code given below. I would also like to run the function z from p. How do I achieve this? function x() { var a = 10; return function y() { var b = 20; return function z() { console.log(a, b); }… Read More How to access grand-child's variable in a closure

console.log([1 , 2, 3 , 4 , 5].map((acc = 0 , num => acc += num))); // output : [1, 3, 6, 10, 15] I know closure has been applied here to this code but don’t know how its working step by step. I want to visualize that. we know the map has this Signature,… Read More Can you explain me the JS code ? How its working?

Consider the following: use std::ops::Fn; fn require_picky_callback( cb : impl Fn() -> () + ‘static) { } fn main() { let s = String::from("Rust"); … let s_copy = s.clone(); let cb = move || { s_copy; }; require_picky_callback(cb); } If String in this example were replaced with a Copy-able type such as int, this example… Read More Inability to capture by Clone prevents some closures from being pure functions that otherwise could/should be. Any workaround?