From 19aa10132cc727c8561730ab096b21d14507c81d Mon Sep 17 00:00:00 2001
From: ljedrz <ljedrz@gmail.com>
Date: Wed, 31 Oct 2018 10:22:22 +0100
Subject: [PATCH] Speed up String::from_utf16

---
 src/liballoc/string.rs | 10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/src/liballoc/string.rs b/src/liballoc/string.rs
index ff3587d5d873..8690f9017c40 100644
--- a/src/liballoc/string.rs
+++ b/src/liballoc/string.rs
@@ -618,7 +618,15 @@ impl String {
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn from_utf16(v: &[u16]) -> Result<String, FromUtf16Error> {
-        decode_utf16(v.iter().cloned()).collect::<Result<_, _>>().map_err(|_| FromUtf16Error(()))
+        let mut ret = String::with_capacity(v.len());
+        for c in decode_utf16(v.iter().cloned()) {
+            if let Ok(c) = c {
+                ret.push(c);
+            } else {
+                return Err(FromUtf16Error(()));
+            }
+        }
+        Ok(ret)
     }
 
     /// Decode a UTF-16 encoded slice `v` into a `String`, replacing