From f8d4cdc170bead42db3ffa647318ecf2bd6430e7 Mon Sep 17 00:00:00 2001
From: Shotaro Yamada <sinkuu@sinkuu.xyz>
Date: Mon, 14 Oct 2019 12:56:18 +0900
Subject: Avoid cloning `Arc<[T]>` into a vec if possible

---
 crates/ra_hir/src/util.rs | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)
 create mode 100644 crates/ra_hir/src/util.rs

(limited to 'crates/ra_hir/src/util.rs')

diff --git a/crates/ra_hir/src/util.rs b/crates/ra_hir/src/util.rs
new file mode 100644
index 000000000..46f423c91
--- /dev/null
+++ b/crates/ra_hir/src/util.rs
@@ -0,0 +1,19 @@
+//! Internal utility functions.
+
+use std::sync::Arc;
+
+/// Helper for mutating `Arc<[T]>` (i.e. `Arc::make_mut` for Arc slices).
+/// The underlying values are cloned if there are other strong references.
+pub(crate) fn make_mut_arc_slice<T: Clone, R>(
+    a: &mut Arc<[T]>,
+    f: impl FnOnce(&mut [T]) -> R,
+) -> R {
+    if let Some(s) = Arc::get_mut(a) {
+        f(s)
+    } else {
+        let mut v = a.to_vec();
+        let r = f(&mut v);
+        *a = Arc::from(v);
+        r
+    }
+}
-- 
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