Implementing collect for Custom Iterators in Rust

Rust's Iterator trait is incredibly powerful, allowing us to process sequences of data lazily and efficiently. A fundamental operation on iterators is collect, which consumes an iterator and transforms its elements into a collection type like Vec, HashMap, or HashSet. This challenge will guide you through implementing your own collect-like functionality for a custom iterator.

Problem Description

Your task is to implement a method, let's call it my_collect, that behaves similarly to Rust's built-in collect method. This method will be defined as an extension trait for any type that implements Iterator. It should be generic enough to allow collecting into various collection types, provided those types can be constructed from an iterator.

Key Requirements:

1. Extension Trait: You need to define an extension trait (e.g., MyCollectExt) that provides the my_collect method.
2. Generic my_collect Method: The my_collect method should be generic over the target collection type C.
3. FromIterator Trait Bound: The target collection type C must implement std::iter::FromIterator<Self::Item>. This trait is what enables a collection to be built from an iterator's elements.
4. Iterator Consumption: The my_collect method must consume the iterator, meaning it will iterate through all its elements until None is returned.
5. Return Collected Type: The method should return an instance of the target collection type C.

Expected Behavior:

The my_collect method should take an iterator and construct a new instance of a specified collection type by adding each item produced by the iterator to it.

Edge Cases:

• Empty Iterators: An empty iterator should result in an empty collection.
• Iterators with Many Elements: The implementation should handle iterators that produce a large number of elements.

Examples

Example 1: Collecting into a Vec

Input: An iterator that yields integers 1, 2, 3.

// Assume `my_collect` is implemented and accessible.
let my_vec: Vec<i32> = (1..=3).my_collect();

Output: vec![1, 2, 3]
Explanation: The iterator `(1..=3)` yields 1, then 2, then 3. `my_collect` consumes these elements and builds a `Vec<i32>` from them.

Example 2: Collecting into a HashSet

Input: An iterator that yields strings "apple", "banana", "apple".

// Assume `my_collect` is implemented and accessible.
use std::collections::HashSet;
let my_set: HashSet<String> = ["apple", "banana", "apple"].iter().map(|s| s.to_string()).my_collect();

Output: A HashSet containing {"apple", "banana"} (order may vary).
Explanation: The iterator yields "apple", "banana", and then "apple" again. `my_collect` builds a `HashSet<String>`, automatically handling duplicate "apple" entries.

Example 3: Collecting into a HashMap

Input: An iterator yielding tuples `(key, value)`.

// Assume `my_collect` is implemented and accessible.
use std::collections::HashMap;
let my_map: HashMap<&str, i32> = [("a", 1), ("b", 2)].iter().copied().my_collect();

Output: A HashMap containing {"a": 1, "b": 2}.
Explanation: The iterator yields the key-value pairs. `my_collect` constructs a `HashMap<&str, i32>` from these pairs.

Constraints

• The solution must be written in Rust.
• The extension trait and my_collect method should be generic and work with any Iterator.
• The target collection C must satisfy the std::iter::FromIterator<Self::Item> trait bound.
• Performance: While not strictly timed, the implementation should be reasonably efficient, avoiding unnecessary cloning or allocations where possible. The approach should mirror the standard library's collect in terms of how it iterates and builds the collection.

Notes

• Recall how Rust's standard library defines extension traits using impl Trait for SomeType and the #[cfg] attribute for conditional compilation.
• Consider the signature of the collect method in the standard library for inspiration. It often has a type annotation on the variable it's assigned to, which helps the compiler infer the target collection type.
• The FromIterator trait is key here. You'll need to leverage its from_iter method within your my_collect implementation.
• The Self::Item associated type of an Iterator represents the type of elements the iterator yields.