I'm learning OCaml and need to understand how to use mutable variables, specifically 'ref cells'. Can you explain what a ref cell is and provide the OCaml code to initialize one with the value 5 and then update its value to 10, based on the 'Real World OCaml' documentation?
Navigate to 'realworldocaml.org'. From the 'Table of Contents', navigate to 'Imperative Programming' under 'Language Concepts'. On the 'Imperative Programming' page, go to 'Mutable Record and Object Fields and Ref Cells' under 'Primitive Mutable Data'. Locate the 'Ref cells' subsection and extract the explanation and relevant OCaml code examples. State the explanation of ref cells and the OCaml code for initializing a ref with 5 and updating it to 10.
The explanation clearly states that 'Ref cells' are used for mutable variables in OCaml, acting as containers for a single mutable value. The provided OCaml code for initializing a ref with the value 5 is `let x = ref 5;;`. The provided OCaml code for updating the ref's value to 10 is `x := 10;;`.