From 1653c86d0c3de39ab1b92847ef4d69a86461b918 Mon Sep 17 00:00:00 2001
From: Brian Koropoff <bkoropoff@gmail.com>
Date: Sat, 2 Aug 2014 13:16:00 -0700
Subject: [PATCH 1/2] Add utility macro to count arguments in a comma-separated
 list

---
 src/libstd/macros.rs | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index e67329df7aec4..1936af87d76e3 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -348,6 +348,15 @@ macro_rules! try(
     ($e:expr) => (match $e { Ok(e) => e, Err(e) => return Err(e) })
 )
 
+/// Expands to an expression which evaluates to the number of
+/// comma-separated expression parameters passed to it.
+#[macro_export]
+macro_rules! count_args(
+    ($e:expr $(,$e_rest:expr)*) => (1u + count_args!($($e_rest),*));
+    () => (0u);
+    ($($e:expr),*,) => (count_args!($($e),*))
+)
+
 /// Create a `std::vec::Vec` containing the arguments.
 #[macro_export]
 macro_rules! vec(

From 224cd1eea936f0f39e63c12541cefa2f4b11e9ee Mon Sep 17 00:00:00 2001
From: Brian Koropoff <bkoropoff@gmail.com>
Date: Sat, 2 Aug 2014 13:17:14 -0700
Subject: [PATCH 2/2] Make vec!() macro create a vector with a precise capacity

---
 src/libstd/macros.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/libstd/macros.rs b/src/libstd/macros.rs
index 1936af87d76e3..e726793a814db 100644
--- a/src/libstd/macros.rs
+++ b/src/libstd/macros.rs
@@ -362,7 +362,7 @@ macro_rules! count_args(
 macro_rules! vec(
     ($($e:expr),*) => ({
         // leading _ to allow empty construction without a warning.
-        let mut _temp = ::std::vec::Vec::new();
+        let mut _temp = ::std::vec::Vec::with_capacity(count_args!($($e),*));
         $(_temp.push($e);)*
         _temp
     });