Avoid allocations when joining strings

components/script/dom/cssstyledeclaration.rs

@@ -15,11 +15,10 @@ use selectors::parser::PseudoElement;
 use std::ascii::AsciiExt;
 use std::borrow::ToOwned;
 use std::cell::Ref;
-use std::slice::SliceConcatExt;
 use string_cache::Atom;
 use style::properties::PropertyDeclaration;
 use style::properties::{is_supported_property, longhands_from_shorthand, parse_one_declaration};
-use util::str::DOMString;
+use util::str::{DOMString, str_join};
 
 // http://dev.w3.org/csswg/cssom/#the-cssstyledeclaration-interface
 #[dom_struct]
@@ -50,8 +49,8 @@ macro_rules! css_properties(
 );
 
 fn serialize_list(list: &[Ref<PropertyDeclaration>]) -> DOMString {
-    let strings: Vec<_> = list.iter().map(|d| d.value()).collect();
-    strings.join(" ")
+    let str_iter = list.iter().map(|d| d.value());
+    str_join(str_iter, " ")
 }
 
 impl CSSStyleDeclaration {

components/script/dom/document.rs

@@ -98,7 +98,7 @@ use std::sync::mpsc::channel;
 use string_cache::{Atom, QualName};
 use time;
 use url::Url;
-use util::str::{DOMString, split_html_space_chars};
+use util::str::{DOMString, split_html_space_chars, str_join};
 
 #[derive(JSTraceable, PartialEq, HeapSizeOf)]
 pub enum IsHTMLDocument {
@@ -1443,7 +1443,7 @@ impl DocumentMethods for Document {
             Some(ref title) => {
                 // Steps 3-4.
                 let value = Node::collect_text_contents(title.r().children());
-                split_html_space_chars(&value).collect::<Vec<_>>().join(" ")
+                str_join(split_html_space_chars(&value), " ")
             },
         }
     }

components/script/dom/htmloptionelement.rs

@@ -18,7 +18,7 @@ use dom::htmlelement::{HTMLElement, HTMLElementTypeId};
 use dom::node::{Node, NodeTypeId};
 use dom::virtualmethods::VirtualMethods;
 use std::cell::Cell;
-use util::str::{DOMString, split_html_space_chars};
+use util::str::{DOMString, split_html_space_chars, str_join};
 
 #[dom_struct]
 pub struct HTMLOptionElement {
@@ -93,8 +93,7 @@ impl HTMLOptionElementMethods for HTMLOptionElement {
         let node = NodeCast::from_ref(self);
         let mut content = String::new();
         collect_text(&node, &mut content);
-        let v: Vec<&str> = split_html_space_chars(&content).collect();
-        v.join(" ")
+        str_join(split_html_space_chars(&content), " ")
     }
 
     // https://www.whatwg.org/html/#dom-option-text

components/script/lib.rs

@@ -24,7 +24,6 @@
 #![feature(str_utf16)]
 #![feature(unicode)]
 #![feature(vec_push_all)]
-#![feature(slice_concat_ext)]
 
 #![deny(unsafe_code)]
 #![allow(non_snake_case)]

components/util/str.rs

@@ -326,8 +326,10 @@ pub unsafe fn c_str_to_string(s: *const c_char) -> String {
     from_utf8(CStr::from_ptr(s).to_bytes()).unwrap().to_owned()
 }
 
-pub fn str_join<T: AsRef<str>>(strs: &[T], join: &str) -> String {
-    strs.iter().fold(String::new(), |mut acc, s| {
+pub fn str_join<I, T>(strs: I, join: &str) -> String
+    where I: IntoIterator<Item=T>, T: AsRef<str>,
+{
+    strs.into_iter().fold(String::new(), |mut acc, s| {
         if !acc.is_empty() { acc.push_str(join); }
         acc.push_str(s.as_ref());
         acc