Why an Interior Mutable abstraction is needed in the Rust core library

Interior mutabiliby is a concept known to anyone who have programmed in Rust for a while. And even though Rust's stdlib have several wrapper-types allowing interior mutability there is no trait unifying these types. Motivated by writing libraries suitable for no_std development that are fully safe to use with threads, this blog post will attempt to fill in one gap in the Rust stdlib.