Option::map(_).flatten() => Option::and_then(_)

[lopopolo]

The map_flatten lint seems to only apply to iterators:

rust-clippy/clippy_lints/src/methods/mod.rs

Lines 406 to 422 in 41d90d3

	declare_clippy_lint! {
	/// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
	///
	/// **Why is this bad?** Readability, this can be written more concisely as a
	/// single method call.
	///
	/// **Known problems:**
	///
	/// **Example:**
	/// ```rust
	/// let vec = vec![vec![1]];
	/// vec.iter().map(|x| x.iter()).flatten();
	/// ```
	pub MAP_FLATTEN,
	pedantic,
	"using combinations of `flatten` and `map` which can usually be written as a single method call"
	}

For Option, map + flatten can be replaced with and_then.

see for example this code:

captures.get(index).map(Option::as_deref).flatten()

which can be more succinctly written as:

captures.get(index).and_then(Option::as_deref)

[flip1995]

This is only the case, when get(..) returns an Option<Option<_>> type, right?

Wait flatten is only implemented for Option<Option<T>>, so it would type error if map would return something other than Option<Option<_>> anyway.

[lopopolo]

In this case get returns an Option<&Option<Vec<u8>>>

[marcin-serwin]

Hi, Could I take a look at this issue?

[flip1995]

Sure, go ahead!