std::io::mem: add a with_capacity constructor to MemWriter.

This allows one to reduce the number of reallocs of the internal buffer
if one has an approximate idea of the size of the final output.

diff --git a/src/libstd/io/mem.rs b/src/libstd/io/mem.rs
index b08f4af9a54c6c3db981e1801ab8fecbb355429d..aa3eb9a83176333bb2a2a04bad37eea7faa77977 100644 (file)
--- a/src/libstd/io/mem.rs
+++ b/src/libstd/io/mem.rs
@@ -27,8 +27,14 @@ pub struct MemWriter {
 }
 
 impl MemWriter {
+    /// Create a new `MemWriter`.
     pub fn new() -> MemWriter {
-        MemWriter { buf: vec::with_capacity(128), pos: 0 }
+        MemWriter::with_capacity(128)
+    }
+    /// Create a new `MemWriter`, allocating at least `n` bytes for
+    /// the internal buffer.
+    pub fn with_capacity(n: uint) -> MemWriter {
+        MemWriter { buf: vec::with_capacity(n), pos: 0 }
     }
 }