I want to declare acceptable_set and use it. But an empty vector is assigned to it. So the compiler warns. How to declare a variable and do not assign it? let mut acceptable_set: Vec<String> = Vec::new(); if opt.acceptable_set.is_none() { acceptable_set = crate::builtin_words::ACCEPTABLE .to_vec() .iter_mut() .map(|x| x.to_string()) .collect(); } else { acceptable_set = get_acceptable_set(opt) } warning:… Read More How to declare a variable but not assign it?

How to properly initialize a struct in Rust, with good enough encapsulations? Or more naively: how to leverage object/instance methods in the initialization/constructing process of structs? For example, as the initialization block in Kotlin: private class BinaryIndexedTree(nums: IntArray) { private val nNums = nums.size private val fenwick = IntArray(nNums + 1) { 0 } //… Read More How to properly initialize a struct in Rust, with good enough encapsulations?

Create an “UnusualClass” class in which direct and copy initialization produce different effects throughout. In particular, the attempt of direct or copy initialization should produce on the screen the print "Direct initialization" or "Copy initialization" #include <iostream> class UnusualClass{ public: UnusualClass(const int &n){ std::cout<<"Copy initialization"; } UnusualClass &operator=(const int &n){ std::cout<<"Direct initialization"; } }; int… Read More Make difference between copy and direct initialization