Rust Option/Result conversion functions

RUST_OPTION_RESULT_CONVERSIONS.md

I used to have a site bookmarked with a table of all these functions, but the link is dead. Here's a matrix of Option and Result conversion functions. These become second nature once you have used Rust for any significant length of time, but it's useful to have a table reference.

For each of the below:

• T is the value possibly contained in an input Ok Result or Some Option.
• U is a new value created by transforming or replacing an input T. Note that when U appears in methods like map, U ?= T, for example by calling Result<T, E>.map(|t| t)
• E is the error possibly contained in an input Err Result
• F is a new value created by transforming or replacing an input E. Note that when F appears in methods like map, F ?= E, for example by calling Result<T, E>.map_err(|e| e)

Input Type	Method	Output Type	Notes
Result<T, E>	and	Result<T, E>	Eager, use and_then instead.
Result<T, E>	and_then	Result<T, E>
Result<T, E>	err	Option<E>
Result<T, E>	map	Result<U, E>
Result<T, E>	map_err	Result<T, F>
Result<T, E>	map_or	U	Eager, use map_or_else instead.
Result<T, E>	map_or_else	U
Result<T, E>	ok	Option<T>
Result<T, E>	or	Result<T, F>	Eager, use or_else instead.
Result<T, E>	or_else	Result<T, F>

Input Type	Method	Output Type	Notes
Option<T>	and	Option<U>	Eager, use and_then instead.
Option<T>	and_then	Option<U>
Option<T>	filter	Option<T>
Option<T>	map	Option<U>
Option<T>	map_or	U	Eager, use map_or_else instead.
Option<T>	map_or_else	U
Option<T>	ok_or	Result<T, E>	Eager, use ok_or_else instead.
Option<T>	ok_or_else	Result<T, E>
Option<T>	or	Option<T>	Eager, use or_else instead.
Option<T>	or_else	Option<T>