auto merge of #19467 : japaric/rust/uc, r=alexcrichton

This PR moves almost all our current uses of closures, both in public API and internal uses, to the new "unboxed" closures system.

In most cases, downstream code that *only uses* closures will continue to work as it is. The reason is that the `|| {}` syntax can be inferred either as a boxed or an "unboxed" closure according to the context. For example the following code will continue to work:

``` rust
some_option.map(|x| x.transform_with(upvar))
```

And will get silently upgraded to an "unboxed" closure.

In some other cases, it may be necessary to "annotate" which `Fn*` trait the closure implements:

```
// Change this
|x| { /* body */}
// to either of these
|: x| { /* body */}  // closure implements the FnOnce trait
|&mut : x| { /* body */}  // FnMut
|&: x| { /* body */}  // Fn
```

This mainly occurs when the closure is assigned to a variable first, and then passed to a function/method.

``` rust
let closure = |: x| x.transform_with(upvar);
some.option.map(closure)
```

(It's very likely that in the future, an improved inference engine will make this annotation unnecessary)

Other cases that require annotation are closures that implement some trait via a blanket `impl`, for example:

- `std::finally::Finally`
- `regex::Replacer`
- `std::str::CharEq`

``` rust
string.trim_left_chars(|c: char| c.is_whitespace())
//~^ ERROR: the trait `Fn<(char,), bool>` is not implemented for the type `|char| -> bool`
string.trim_left_chars(|&: c: char| c.is_whitespace())  // OK
```

Finally, all implementations of traits that contain boxed closures in the arguments of their methods are now broken. And will need to be updated to use unboxed closures. These are the main affected traits:

- `serialize::Decoder`
- `serialize::DecoderHelpers`
- `serialize::Encoder`
- `serialize::EncoderHelpers`
- `rustrt::ToCStr`

For example, change this:

``` rust
// libserialize/json.rs
impl<'a> Encoder<io::IoError> for Encoder<'a> {
    fn emit_enum(&mut self,
                 _name: &str,
                 f: |&mut Encoder<'a>| -> EncodeResult) -> EncodeResult {
        f(self)
    }
}
```

to:

``` rust
// libserialize/json.rs
impl<'a> Encoder<io::IoError> for Encoder<'a> {
    fn emit_enum<F>(&mut self, _name: &str, f: F) -> EncodeResult where
        F: FnOnce(&mut Encoder<'a>) -> EncodeResult
    {
        f(self)
    }
}
```

[breaking-change]

---

### How the `Fn*` bound has been selected

I've chosen the bounds to make the functions/structs as "generic as possible", i.e. to let them allow the maximum amount of input.

- An `F: FnOnce` bound accepts the three kinds of closures: `|:|`, `|&mut:|` and `|&:|`.
- An `F: FnMut` bound only accepts "non-consuming" closures: `|&mut:|` and `|&:|`.
- An `F: Fn` bound only accept the "immutable environment" closures: `|&:|`.

This means that whenever possible the `FnOnce` bound has been used, if the `FnOnce` bound couldn't be used, then the `FnMut` was used. The `Fn` bound was never used in the whole repository.

The `FnMut` bound was the most used, because it resembles the semantics of the current boxed closures: the closure can modify its environment, and the closure may be called several times.

The `FnOnce` bound allows new semantics: you can move out the upvars when the closure is called. This can be effectively paired with the `move || {}` syntax to transfer ownership from the environment to the closure caller.

In the case of trait methods, is hard to select the "right" bound since we can't control how the trait may be implemented by downstream users. In these cases, I have selected the bound based on how we use these traits in the repository. For this reason the selected bounds may not be ideal, and may require tweaking before stabilization.

r? @aturon

1 files changed, 60 insertions, 29 deletions

diff --git a/src/libcore/str.rs b/src/libcore/str.rs
index d0c8558b55d..92f82bd9771 100644
--- a/src/libcore/str.rs
+++ b/src/libcore/str.rs
@@ -31,6 +31,7 @@ use mem;
 use num::Int;
 use option::Option;
 use option::Option::{None, Some};
+use ops::FnMut;
 use ptr::RawPtr;
 use raw::{Repr, Slice};
 use slice::{mod, SlicePrelude};
@@ -136,15 +137,7 @@ impl CharEq for char {
     fn only_ascii(&self) -> bool { (*self as uint) < 128 }
 }
 
-impl<'a> CharEq for |char|: 'a -> bool {
-    #[inline]
-    fn matches(&mut self, c: char) -> bool { (*self)(c) }
-
-    #[inline]
-    fn only_ascii(&self) -> bool { false }
-}
-
-impl CharEq for extern "Rust" fn(char) -> bool {
+impl<F> CharEq for F where F: FnMut(char) -> bool {
     #[inline]
     fn matches(&mut self, c: char) -> bool { (*self)(c) }
 
@@ -323,8 +316,7 @@ impl<'a> DoubleEndedIterator<(uint, char)> for CharOffsets<'a> {
 
 /// External iterator for a string's bytes.
 /// Use with the `std::iter` module.
-pub type Bytes<'a> =
-    Map<'a, &'a u8, u8, slice::Items<'a, u8>>;
+pub type Bytes<'a> = Map<&'a u8, u8, slice::Items<'a, u8>, fn(&u8) -> u8>;
 
 /// An iterator over the substrings of a string, separated by `sep`.
 #[deriving(Clone)]
@@ -349,8 +341,7 @@ pub struct CharSplitsN<'a, Sep> {
 }
 
 /// An iterator over the lines of a string, separated by either `\n` or (`\r\n`).
-pub type AnyLines<'a> =
-    Map<'a, &'a str, &'a str, CharSplits<'a, char>>;
+pub type AnyLines<'a> = Map<&'a str, &'a str, CharSplits<'a, char>, fn(&str) -> &str>;
 
 impl<'a, Sep> CharSplits<'a, Sep> {
     #[inline]
@@ -1361,10 +1352,13 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// let v: Vec<&str> = "Mary had a little lamb".split(' ').collect();
     /// assert_eq!(v, vec!["Mary", "had", "a", "little", "lamb"]);
     ///
-    /// let v: Vec<&str> = "abc1def2ghi".split(|c: char| c.is_numeric()).collect();
+    /// let v: Vec<&str> = "abc1def2ghi".split(|&: c: char| c.is_numeric()).collect();
     /// assert_eq!(v, vec!["abc", "def", "ghi"]);
     ///
     /// let v: Vec<&str> = "lionXXtigerXleopard".split('X').collect();
@@ -1372,6 +1366,7 @@ pub trait StrPrelude for Sized? {
     ///
     /// let v: Vec<&str> = "".split('X').collect();
     /// assert_eq!(v, vec![""]);
+    /// # }
     /// ```
     fn split<'a, Sep: CharEq>(&'a self, sep: Sep) -> CharSplits<'a, Sep>;
 
@@ -1382,10 +1377,13 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// let v: Vec<&str> = "Mary had a little lambda".splitn(2, ' ').collect();
     /// assert_eq!(v, vec!["Mary", "had", "a little lambda"]);
     ///
-    /// let v: Vec<&str> = "abc1def2ghi".splitn(1, |c: char| c.is_numeric()).collect();
+    /// let v: Vec<&str> = "abc1def2ghi".splitn(1, |&: c: char| c.is_numeric()).collect();
     /// assert_eq!(v, vec!["abc", "def2ghi"]);
     ///
     /// let v: Vec<&str> = "lionXXtigerXleopard".splitn(2, 'X').collect();
@@ -1396,6 +1394,7 @@ pub trait StrPrelude for Sized? {
     ///
     /// let v: Vec<&str> = "".splitn(1, 'X').collect();
     /// assert_eq!(v, vec![""]);
+    /// # }
     /// ```
     fn splitn<'a, Sep: CharEq>(&'a self, count: uint, sep: Sep) -> CharSplitsN<'a, Sep>;
 
@@ -1408,6 +1407,9 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// let v: Vec<&str> = "A.B.".split_terminator('.').collect();
     /// assert_eq!(v, vec!["A", "B"]);
     ///
@@ -1417,11 +1419,12 @@ pub trait StrPrelude for Sized? {
     /// let v: Vec<&str> = "Mary had a little lamb".split(' ').rev().collect();
     /// assert_eq!(v, vec!["lamb", "little", "a", "had", "Mary"]);
     ///
-    /// let v: Vec<&str> = "abc1def2ghi".split(|c: char| c.is_numeric()).rev().collect();
+    /// let v: Vec<&str> = "abc1def2ghi".split(|&: c: char| c.is_numeric()).rev().collect();
     /// assert_eq!(v, vec!["ghi", "def", "abc"]);
     ///
     /// let v: Vec<&str> = "lionXXtigerXleopard".split('X').rev().collect();
     /// assert_eq!(v, vec!["leopard", "tiger", "", "lion"]);
+    /// # }
     /// ```
     fn split_terminator<'a, Sep: CharEq>(&'a self, sep: Sep) -> CharSplits<'a, Sep>;
 
@@ -1432,14 +1435,18 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// let v: Vec<&str> = "Mary had a little lamb".rsplitn(2, ' ').collect();
     /// assert_eq!(v, vec!["lamb", "little", "Mary had a"]);
     ///
-    /// let v: Vec<&str> = "abc1def2ghi".rsplitn(1, |c: char| c.is_numeric()).collect();
+    /// let v: Vec<&str> = "abc1def2ghi".rsplitn(1, |&: c: char| c.is_numeric()).collect();
     /// assert_eq!(v, vec!["ghi", "abc1def"]);
     ///
     /// let v: Vec<&str> = "lionXXtigerXleopard".rsplitn(2, 'X').collect();
     /// assert_eq!(v, vec!["leopard", "tiger", "lionX"]);
+    /// # }
     /// ```
     fn rsplitn<'a, Sep: CharEq>(&'a self, count: uint, sep: Sep) -> CharSplitsN<'a, Sep>;
 
@@ -1650,10 +1657,14 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// assert_eq!("11foo1bar11".trim_chars('1'), "foo1bar")
     /// let x: &[_] = &['1', '2'];
     /// assert_eq!("12foo1bar12".trim_chars(x), "foo1bar")
-    /// assert_eq!("123foo1bar123".trim_chars(|c: char| c.is_numeric()), "foo1bar")
+    /// assert_eq!("123foo1bar123".trim_chars(|&: c: char| c.is_numeric()), "foo1bar")
+    /// # }
     /// ```
     fn trim_chars<'a, C: CharEq>(&'a self, to_trim: C) -> &'a str;
 
@@ -1666,10 +1677,14 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// assert_eq!("11foo1bar11".trim_left_chars('1'), "foo1bar11")
     /// let x: &[_] = &['1', '2'];
     /// assert_eq!("12foo1bar12".trim_left_chars(x), "foo1bar12")
-    /// assert_eq!("123foo1bar123".trim_left_chars(|c: char| c.is_numeric()), "foo1bar123")
+    /// assert_eq!("123foo1bar123".trim_left_chars(|&: c: char| c.is_numeric()), "foo1bar123")
+    /// # }
     /// ```
     fn trim_left_chars<'a, C: CharEq>(&'a self, to_trim: C) -> &'a str;
 
@@ -1682,10 +1697,14 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// assert_eq!("11foo1bar11".trim_right_chars('1'), "11foo1bar")
     /// let x: &[_] = &['1', '2'];
     /// assert_eq!("12foo1bar12".trim_right_chars(x), "12foo1bar")
-    /// assert_eq!("123foo1bar123".trim_right_chars(|c: char| c.is_numeric()), "123foo1bar")
+    /// assert_eq!("123foo1bar123".trim_right_chars(|&: c: char| c.is_numeric()), "123foo1bar")
+    /// # }
     /// ```
     fn trim_right_chars<'a, C: CharEq>(&'a self, to_trim: C) -> &'a str;
 
@@ -1826,17 +1845,21 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// let s = "Löwe 老虎 Léopard";
     ///
     /// assert_eq!(s.find('L'), Some(0));
     /// assert_eq!(s.find('é'), Some(14));
     ///
     /// // the first space
-    /// assert_eq!(s.find(|c: char| c.is_whitespace()), Some(5));
+    /// assert_eq!(s.find(|&: c: char| c.is_whitespace()), Some(5));
     ///
     /// // neither are found
     /// let x: &[_] = &['1', '2'];
     /// assert_eq!(s.find(x), None);
+    /// # }
     /// ```
     fn find<C: CharEq>(&self, search: C) -> Option<uint>;
 
@@ -1851,17 +1874,21 @@ pub trait StrPrelude for Sized? {
     /// # Example
     ///
     /// ```rust
+    /// # #![feature(unboxed_closures)]
+    ///
+    /// # fn main() {
     /// let s = "Löwe 老虎 Léopard";
     ///
     /// assert_eq!(s.rfind('L'), Some(13));
     /// assert_eq!(s.rfind('é'), Some(14));
     ///
     /// // the second space
-    /// assert_eq!(s.rfind(|c: char| c.is_whitespace()), Some(12));
+    /// assert_eq!(s.rfind(|&: c: char| c.is_whitespace()), Some(12));
     ///
     /// // searches for an occurrence of either `1` or `2`, but neither are found
     /// let x: &[_] = &['1', '2'];
     /// assert_eq!(s.rfind(x), None);
+    /// # }
     /// ```
     fn rfind<C: CharEq>(&self, search: C) -> Option<uint>;
 
@@ -1980,7 +2007,9 @@ impl StrPrelude for str {
 
     #[inline]
     fn bytes(&self) -> Bytes {
-        self.as_bytes().iter().map(|&b| b)
+        fn deref(&x: &u8) -> u8 { x }
+
+        self.as_bytes().iter().map(deref)
     }
 
     #[inline]
@@ -2053,11 +2082,13 @@ impl StrPrelude for str {
     }
 
     fn lines_any(&self) -> AnyLines {
-        self.lines().map(|line| {
+        fn f(line: &str) -> &str {
             let l = line.len();
             if l > 0 && line.as_bytes()[l - 1] == b'\r' { line.slice(0, l - 1) }
             else { line }
-        })
+        }
+
+        self.lines().map(f)
     }
 
     #[inline]
@@ -2140,11 +2171,11 @@ impl StrPrelude for str {
 
     #[inline]
     fn trim_chars<C: CharEq>(&self, mut to_trim: C) -> &str {
-        let cur = match self.find(|c: char| !to_trim.matches(c)) {
+        let cur = match self.find(|&mut: c: char| !to_trim.matches(c)) {
             None => "",
             Some(i) => unsafe { self.slice_unchecked(i, self.len()) }
         };
-        match cur.rfind(|c: char| !to_trim.matches(c)) {
+        match cur.rfind(|&mut: c: char| !to_trim.matches(c)) {
             None => "",
             Some(i) => {
                 let right = cur.char_range_at(i).next;
@@ -2155,7 +2186,7 @@ impl StrPrelude for str {
 
     #[inline]
     fn trim_left_chars<C: CharEq>(&self, mut to_trim: C) -> &str {
-        match self.find(|c: char| !to_trim.matches(c)) {
+        match self.find(|&mut: c: char| !to_trim.matches(c)) {
             None => "",
             Some(first) => unsafe { self.slice_unchecked(first, self.len()) }
         }
@@ -2163,7 +2194,7 @@ impl StrPrelude for str {
 
     #[inline]
     fn trim_right_chars<C: CharEq>(&self, mut to_trim: C) -> &str {
-        match self.rfind(|c: char| !to_trim.matches(c)) {
+        match self.rfind(|&mut: c: char| !to_trim.matches(c)) {
             None => "",
             Some(last) => {
                 let next = self.char_range_at(last).next;