Add constraints that must be upheld to use an item.

A future represents an asynchronous computation obtained by use of `async`.

Bind a value to a variable.

Make an item visible to others.

A hash set implemented as a `HashMap` where the value is `()`.

`Request` supports generic, type-driven access to data. Its use is currently restricted to the standard library in cases where trait authors wish to allow trait implementors to share generic information across trait boundaries. The motivating and prototypical use case is `core::error::Error` which would otherwise require a method per concrete type (eg. `std::backtrace::Backtrace` instance that implementors want to expose to users).

A view into an occupied entry in a `HashMap`. It is part of the `RawEntryMut` enum.

The error type for operations on the `PATH` variable. Possibly returned from `env::join_paths()`.

A struct to help with `fmt::Debug` implementations.

An iterator over the lines of an instance of `BufRead`.