Rust on StackOverflow: Frequent duplicates
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### Useful links
- [Top 100 Most Duplicated Rust Questions](https://data.stackexchange.com/stackoverflow/query/1350611/most-duplicated-rust-questions) (Data Explorer)
- [Frequently linked questions](https://stackoverflow.com/questions/tagged/rust?sort=frequent&pageSize=50) (this doesn't have to be "linked as duplicate", but includes every kind of linking)

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### New questions
- [What are the valid path roots in the `use` keyword?](https://stackoverflow.com/questions/54289071/what-are-the-valid-path-roots-in-the-use-keyword)
- [Unable to read file contents to string - `Result` does not implement any method in scope named `read_to_string`](https://stackoverflow.com/questions/29214963/unable-to-read-file-contents-to-string-result-does-not-implement-any-method-in)
- Regarding `print!` being line buffered:
- [print! macro gets executed out of order](https://stackoverflow.com/questions/49607156/print-macro-gets-executed-out-of-order/49607772)
- [Why does this read input before printing?](https://stackoverflow.com/questions/34993744/why-does-this-read-input-before-printing)
- [How do I print output without a trailing newline in Rust?](https://stackoverflow.com/questions/37531903/how-do-i-print-output-without-a-trailing-newline-in-rust)

### Linked a lot already
- [Why can't I store a value and a reference to that value in the same struct?](https://stackoverflow.com/questions/32300132/why-cant-i-store-a-value-and-a-reference-to-that-value-in-the-same-struct)
- [Return local String as a slice (`&str`)](https://stackoverflow.com/q/29428227)
- [Is there any way to return a reference to a variable created in a function?](https://stackoverflow.com/questions/32682876/is-there-any-way-to-return-a-reference-to-a-variable-created-in-a-function)
- ["Expected type parameter" error in the constructor of a generic struct](https://stackoverflow.com/q/32551177)
- [Why is it discouraged to accept a reference to a String (&String), Vec (&Vec), or Box (&Box) as a function argument?](https://stackoverflow.com/questions/40006219/why-is-it-discouraged-to-accept-a-reference-to-a-string-string-vec-vec-o)
- [Cannot obtain a mutable reference when iterating a recursive structure: cannot borrow as mutable more than once at a time](https://stackoverflow.com/q/37986640)
- [Why do `try!()` and `?` not compile when used in a function that doesn't return `Option` or `Result`?](https://stackoverflow.com/q/30555477)
- [How to lookup from and insert into a `HashMap` efficiently?](https://stackoverflow.com/q/28512394)
- [Unexpected value when reading user input from stdin
](https://stackoverflow.com/q/27773313) (newline trim)
- [How can I pass a reference to a stack variable to a thread?](https://stackoverflow.com/q/32750829)
- [How can you make a safe static singleton in Rust?](https://stackoverflow.com/q/27221504)
- [How do I create a global, mutable singleton?](https://stackoverflow.com/q/27791532)
- [Why doesn't Rust support trait object upcasting?](https://stackoverflow.com/q/28632968)
- [Why is a trait not implemented for a type that clearly has it implemented?](https://stackoverflow.com/q/44437123)
- [How do I create a heterogeneous collection of objects?](https://stackoverflow.com/q/27957103)
- [How to get mutable references to two array elements at the same time?](https://stackoverflow.com/q/30073684)
- [Rust borrow of a HashMap lasts beyond the scope it's in?](https://stackoverflow.com/q/38023871)
- [How can I swap in a new value for a field in a mutable reference to a structure?](https://stackoverflow.com/q/27098694)
- [How do I implement a trait I don't own for a type I don't own?](https://stackoverflow.com/q/25413201)
- [Why is this match pattern unreachable when using non-literal patterns?](https://stackoverflow.com/q/28225958)
- [How do I require a generic type implement an operation like Add, Sub, Mul, or Div in a generic function?](https://stackoverflow.com/q/29184358)
- [Mutably borrow one struct field while borrowing another in a closure](https://stackoverflow.com/q/36379242)
- [Deriving a trait results in unexpected compiler error, but the manual implementation works](https://stackoverflow.com/q/39415052)
- [Cannot borrow as immutable because it is also borrowed as mutable in function arguments](https://stackoverflow.com/q/41187296)