add FlatOk trait to Result/Option suite

Signed-off-by: Jason Volk <jason@zemos.net>

src/core/result/flat_ok.rs

@@ -0,0 +1,34 @@
+use super::Result;
+
+pub trait FlatOk<T> {
+	/// Equivalent to .transpose().ok().flatten()
+	fn flat_ok(self) -> Option<T>;
+
+	/// Equivalent to .transpose().ok().flatten().ok_or(...)
+	fn flat_ok_or<E>(self, err: E) -> Result<T, E>;
+
+	/// Equivalent to .transpose().ok().flatten().ok_or_else(...)
+	fn flat_ok_or_else<E, F: FnOnce() -> E>(self, err: F) -> Result<T, E>;
+}
+
+impl<T, E> FlatOk<T> for Option<Result<T, E>> {
+	#[inline]
+	fn flat_ok(self) -> Option<T> { self.transpose().ok().flatten() }
+
+	#[inline]
+	fn flat_ok_or<Ep>(self, err: Ep) -> Result<T, Ep> { self.flat_ok().ok_or(err) }
+
+	#[inline]
+	fn flat_ok_or_else<Ep, F: FnOnce() -> Ep>(self, err: F) -> Result<T, Ep> { self.flat_ok().ok_or_else(err) }
+}
+
+impl<T, E> FlatOk<T> for Result<Option<T>, E> {
+	#[inline]
+	fn flat_ok(self) -> Option<T> { self.ok().flatten() }
+
+	#[inline]
+	fn flat_ok_or<Ep>(self, err: Ep) -> Result<T, Ep> { self.flat_ok().ok_or(err) }
+
+	#[inline]
+	fn flat_ok_or_else<Ep, F: FnOnce() -> Ep>(self, err: F) -> Result<T, Ep> { self.flat_ok().ok_or_else(err) }
+}