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-# Weak and Circle reference

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-# Crate

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 # Why Exercise.rs
+> 中文版 [传送门](https://zh.exercise.rs)
+
+Greetings and welcome to `exercise.rs`， If you have the following problems: 
+
+- After learning some rust knowledge, you want to take a step:  do some exercises, but found unchallenging ones
+- Found nothing about rust toolchains, std, ascyn/.await topics
+- Still have no idea of what to do next, maybe you tried writing a demo /project, but... not that good or even worse: failed
+
+Then you have come to a right place: here you can find a bunch of easy to hard exercises to improve your Rust skills，this will help you fill the gap of easy-to-learn and hard-to-use.
+
+## About exercises
+- difficulty level: easy: 🌟  medium: 🌟🌟 hard: 🌟🌟🌟  hell: 🌟🌟🌟🌟
+- Everything is online: reading, editing, testing 
+  
+## Contributing
+We welcome all kinds of contributors, especially ones who has precious exercises.
+
+Every exercise you have contributed will be annotated with your nickname and personal link, it's time to show yourself to the world!
+
+## Learning Rust
+If you are a first-time Rust learner, here are some high quality learning resources :
+- [The Book](https://doc.rust-lang.org/book/index.html) for English  speakers
+- [Rust语言圣经(The Course)](https://course.rs) for Chinese speakers, it covers nearly all the topics in Rust
+
+
+## difference to rustlings
+[Rustlings](https://github.com/rust-lang/rustlings) only contains small and easy exercises for junior rust devs. There is a big gap between learning Rust and using it in your projects.
+
+Another limit for rustlings is that you have to download rustlings to local machine and compile it first before starting to learn.
+
+## difference to rust by example
+[Rust By Example](https://doc.rust-lang.org/stable/rust-by-example/) is an excellent online book for learning Rust，`exercise.rs` has some small advantages in :
+
+- more topics and exercises，specially for the hard part of Rust，e.g lifetime、smart pointers、threads 、async/.await etc
+- difficulty from easy to hard，it will minimize the gap between learning and using in projects
+- up-to-date, e.g features which added in Rust 1.58 also have the corresponding exercises in `exercise.rs`
+- Both `course.rs` and `exercise.rs` are designed according to the CS courses in college，so quliaty is the most important factor
+