1 files changed, 54 insertions, 0 deletions

diff --git a/crates/ra_hir_expand/src/either.rs b/crates/ra_hir_expand/src/either.rs
new file mode 100644
index 000000000..83583ef8b
--- /dev/null
+++ b/crates/ra_hir_expand/src/either.rs
@@ -0,0 +1,54 @@
+//! FIXME: write short doc here
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
+pub enum Either<A, B> {
+    A(A),
+    B(B),
+}
+
+impl<A, B> Either<A, B> {
+    pub fn either<R, F1, F2>(self, f1: F1, f2: F2) -> R
+    where
+        F1: FnOnce(A) -> R,
+        F2: FnOnce(B) -> R,
+    {
+        match self {
+            Either::A(a) => f1(a),
+            Either::B(b) => f2(b),
+        }
+    }
+    pub fn map<U, V, F1, F2>(self, f1: F1, f2: F2) -> Either<U, V>
+    where
+        F1: FnOnce(A) -> U,
+        F2: FnOnce(B) -> V,
+    {
+        match self {
+            Either::A(a) => Either::A(f1(a)),
+            Either::B(b) => Either::B(f2(b)),
+        }
+    }
+    pub fn map_a<U, F>(self, f: F) -> Either<U, B>
+    where
+        F: FnOnce(A) -> U,
+    {
+        self.map(f, |it| it)
+    }
+    pub fn a(self) -> Option<A> {
+        match self {
+            Either::A(it) => Some(it),
+            Either::B(_) => None,
+        }
+    }
+    pub fn b(self) -> Option<B> {
+        match self {
+            Either::A(_) => None,
+            Either::B(it) => Some(it),
+        }
+    }
+    pub fn as_ref(&self) -> Either<&A, &B> {
+        match self {
+            Either::A(it) => Either::A(it),
+            Either::B(it) => Either::B(it),
+        }
+    }
+}