---

yaml
---
r: 187355
b: refs/heads/try
c: c51c377
h: refs/heads/master
i:
  187353: d33dd0c
  187351: a95df7f
v: v3

Author: Manishearth

[refs]

@@ -2,7 +2,7 @@
 refs/heads/master: b4c965ee803a4521d8b4575f634e036f93e408f3
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: 3a96d6a9818fe2affc98a187fb1065120458cee9
-refs/heads/try: 0bea550a2a78eba05533f333cc2a0e7f9b5b44e8
+refs/heads/try: c51c377982694d1ed3d545099f4262635defb284
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/dist-snap: ba4081a5a8573875fed17545846f6f6902c8ba8d
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596

branches/try/src/doc/trpl/error-handling.md

@@ -223,6 +223,78 @@ let input = io::stdin().read_line()
                        .ok()
                        .expect("Failed to read line");
 ```
+
 `ok()` converts the `IoResult` into an `Option`, and `expect()` does the same
 thing as `unwrap()`, but takes a message. This message is passed along to the
 underlying `panic!`, providing a better error message if the code errors.
+
+# Using `try!`
+
+When writing code that calls many functions that return the `Result` type, the
+error handling can be tedious. The `try!` macro hides some of the boilerplate
+of propagating errors up the call stack.
+
+It replaces this:
+
+```rust
+use std::fs::File;
+use std::io;
+use std::io::prelude::*;
+
+struct Info {
+    name: String,
+    age: i32,
+    rating: i32,
+}
+
+fn write_info(info: &Info) -> io::Result<()> {
+    let mut file = File::open("my_best_friends.txt").unwrap();
+
+    if let Err(e) = writeln!(&mut file, "name: {}", info.name) {
+        return Err(e)
+    }
+    if let Err(e) = writeln!(&mut file, "age: {}", info.age) {
+        return Err(e)
+    }
+    if let Err(e) = writeln!(&mut file, "rating: {}", info.rating) {
+        return Err(e)
+    }
+
+    return Ok(());
+}
+```
+
+With this:
+
+```rust
+use std::fs::File;
+use std::io;
+use std::io::prelude::*;
+
+struct Info {
+    name: String,
+    age: i32,
+    rating: i32,
+}
+
+fn write_info(info: &Info) -> io::Result<()> {
+    let mut file = try!(File::open("my_best_friends.txt"));
+
+    try!(writeln!(&mut file, "name: {}", info.name));
+    try!(writeln!(&mut file, "age: {}", info.age));
+    try!(writeln!(&mut file, "rating: {}", info.rating));
+
+    return Ok(());
+}
+```
+
+Wrapping an expression in `try!` will result in the unwrapped success (`Ok`)
+value, unless the result is `Err`, in which case `Err` is returned early from
+the enclosing function.
+
+It's worth noting that you can only use `try!` from a function that returns a
+`Result`, which means that you cannot use `try!` inside of `main()`, because
+`main()` doesn't return anything.
+
+`try!` makes use of [`FromError`](../std/error/#the-fromerror-trait) to determine
+what to return in the error case.

branches/try/src/doc/trpl/macros.md

@@ -73,7 +73,7 @@ macro_rules! vec {
     };
 }
 # fn main() {
-#     assert_eq!(&[1,2,3], &vec![1,2,3]);
+#     assert_eq!([1,2,3], vec![1,2,3]);
 # }
 ```
 

branches/try/src/libcollections/binary_heap.rs

@@ -480,7 +480,7 @@ impl<T: Ord> BinaryHeap<T> {
     /// heap.push(3);
     ///
     /// let vec = heap.into_sorted_vec();
-    /// assert_eq!(vec, vec![1, 2, 3, 4, 5, 6, 7]);
+    /// assert_eq!(vec, [1, 2, 3, 4, 5, 6, 7]);
     /// ```
     pub fn into_sorted_vec(mut self) -> Vec<T> {
         let mut end = self.len();

branches/try/src/libcollections/bit.rs

@@ -640,13 +640,13 @@ impl BitVec {
     /// let mut bv = BitVec::from_elem(3, true);
     /// bv.set(1, false);
     ///
-    /// assert_eq!(bv.to_bytes(), vec!(0b10100000));
+    /// assert_eq!(bv.to_bytes(), [0b10100000]);
     ///
     /// let mut bv = BitVec::from_elem(9, false);
     /// bv.set(2, true);
     /// bv.set(8, true);
     ///
-    /// assert_eq!(bv.to_bytes(), vec!(0b00100000, 0b10000000));
+    /// assert_eq!(bv.to_bytes(), [0b00100000, 0b10000000]);
     /// ```
     pub fn to_bytes(&self) -> Vec<u8> {
         fn bit(bit_vec: &BitVec, byte: usize, bit: usize) -> u8 {
@@ -806,7 +806,7 @@ impl BitVec {
     /// let mut bv = BitVec::from_bytes(&[0b01001011]);
     /// bv.grow(2, true);
     /// assert_eq!(bv.len(), 10);
-    /// assert_eq!(bv.to_bytes(), vec!(0b01001011, 0b11000000));
+    /// assert_eq!(bv.to_bytes(), [0b01001011, 0b11000000]);
     /// ```
     pub fn grow(&mut self, n: usize, value: bool) {
         // Note: we just bulk set all the bits in the last word in this fn in multiple places
@@ -2285,12 +2285,12 @@ mod tests {
     fn test_to_bytes() {
         let mut bv = BitVec::from_elem(3, true);
         bv.set(1, false);
-        assert_eq!(bv.to_bytes(), vec!(0b10100000));
+        assert_eq!(bv.to_bytes(), [0b10100000]);
 
         let mut bv = BitVec::from_elem(9, false);
         bv.set(2, true);
         bv.set(8, true);
-        assert_eq!(bv.to_bytes(), vec!(0b00100000, 0b10000000));
+        assert_eq!(bv.to_bytes(), [0b00100000, 0b10000000]);
     }
 
     #[test]
@@ -2675,7 +2675,7 @@ mod bit_set_test {
         let bit_vec: BitSet = usizes.into_iter().collect();
 
         let idxs: Vec<_> = bit_vec.iter().collect();
-        assert_eq!(idxs, vec![0, 2, 3]);
+        assert_eq!(idxs, [0, 2, 3]);
 
         let long: BitSet = (0..10000).filter(|&n| n % 2 == 0).collect();
         let real: Vec<_> = range_step(0, 10000, 2).collect();

branches/try/src/libcollections/btree/map.rs

@@ -1281,7 +1281,7 @@ impl<K, V> BTreeMap<K, V> {
     /// a.insert(2, "b");
     ///
     /// let keys: Vec<usize> = a.keys().cloned().collect();
-    /// assert_eq!(keys, vec![1,2,]);
+    /// assert_eq!(keys, [1, 2]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn keys<'a>(&'a self) -> Keys<'a, K, V> {
@@ -1303,7 +1303,7 @@ impl<K, V> BTreeMap<K, V> {
     /// a.insert(2, "b");
     ///
     /// let values: Vec<&str> = a.values().cloned().collect();
-    /// assert_eq!(values, vec!["a","b"]);
+    /// assert_eq!(values, ["a", "b"]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn values<'a>(&'a self) -> Values<'a, K, V> {

branches/try/src/libcollections/btree/set.rs

@@ -121,7 +121,7 @@ impl<T> BTreeSet<T> {
     /// }
     ///
     /// let v: Vec<usize> = set.iter().cloned().collect();
-    /// assert_eq!(v, vec![1,2,3,4]);
+    /// assert_eq!(v, [1, 2, 3, 4]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn iter(&self) -> Iter<T> {
@@ -138,7 +138,7 @@ impl<T> BTreeSet<T> {
     /// let set: BTreeSet<usize> = [1, 2, 3, 4].iter().cloned().collect();
     ///
     /// let v: Vec<usize> = set.into_iter().collect();
-    /// assert_eq!(v, vec![1,2,3,4]);
+    /// assert_eq!(v, [1, 2, 3, 4]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn into_iter(self) -> IntoIter<T> {
@@ -197,7 +197,7 @@ impl<T: Ord> BTreeSet<T> {
     /// b.insert(3);
     ///
     /// let diff: Vec<usize> = a.difference(&b).cloned().collect();
-    /// assert_eq!(diff, vec![1]);
+    /// assert_eq!(diff, [1]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn difference<'a>(&'a self, other: &'a BTreeSet<T>) -> Difference<'a, T> {
@@ -220,7 +220,7 @@ impl<T: Ord> BTreeSet<T> {
     /// b.insert(3);
     ///
     /// let sym_diff: Vec<usize> = a.symmetric_difference(&b).cloned().collect();
-    /// assert_eq!(sym_diff, vec![1,3]);
+    /// assert_eq!(sym_diff, [1, 3]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn symmetric_difference<'a>(&'a self, other: &'a BTreeSet<T>)
@@ -244,7 +244,7 @@ impl<T: Ord> BTreeSet<T> {
     /// b.insert(3);
     ///
     /// let intersection: Vec<usize> = a.intersection(&b).cloned().collect();
-    /// assert_eq!(intersection, vec![2]);
+    /// assert_eq!(intersection, [2]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn intersection<'a>(&'a self, other: &'a BTreeSet<T>)
@@ -266,7 +266,7 @@ impl<T: Ord> BTreeSet<T> {
     /// b.insert(2);
     ///
     /// let union: Vec<usize> = a.union(&b).cloned().collect();
-    /// assert_eq!(union, vec![1,2]);
+    /// assert_eq!(union, [1, 2]);
     /// ```
     #[stable(feature = "rust1", since = "1.0.0")]
     pub fn union<'a>(&'a self, other: &'a BTreeSet<T>) -> Union<'a, T> {
@@ -534,7 +534,7 @@ impl<'a, 'b, T: Ord + Clone> Sub<&'b BTreeSet<T>> for &'a BTreeSet<T> {
     ///
     /// let result = &a - &b;
     /// let result_vec: Vec<_> = result.into_iter().collect();
-    /// assert_eq!(result_vec, vec![1, 2]);
+    /// assert_eq!(result_vec, [1, 2]);
     /// ```
     fn sub(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
         self.difference(rhs).cloned().collect()
@@ -557,7 +557,7 @@ impl<'a, 'b, T: Ord + Clone> BitXor<&'b BTreeSet<T>> for &'a BTreeSet<T> {
     ///
     /// let result = &a ^ &b;
     /// let result_vec: Vec<_> = result.into_iter().collect();
-    /// assert_eq!(result_vec, vec![1, 4]);
+    /// assert_eq!(result_vec, [1, 4]);
     /// ```
     fn bitxor(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
         self.symmetric_difference(rhs).cloned().collect()
@@ -580,7 +580,7 @@ impl<'a, 'b, T: Ord + Clone> BitAnd<&'b BTreeSet<T>> for &'a BTreeSet<T> {
     ///
     /// let result = &a & &b;
     /// let result_vec: Vec<_> = result.into_iter().collect();
-    /// assert_eq!(result_vec, vec![2, 3]);
+    /// assert_eq!(result_vec, [2, 3]);
     /// ```
     fn bitand(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
         self.intersection(rhs).cloned().collect()
@@ -603,7 +603,7 @@ impl<'a, 'b, T: Ord + Clone> BitOr<&'b BTreeSet<T>> for &'a BTreeSet<T> {
     ///
     /// let result = &a | &b;
     /// let result_vec: Vec<_> = result.into_iter().collect();
-    /// assert_eq!(result_vec, vec![1, 2, 3, 4, 5]);
+    /// assert_eq!(result_vec, [1, 2, 3, 4, 5]);
     /// ```
     fn bitor(self, rhs: &BTreeSet<T>) -> BTreeSet<T> {
         self.union(rhs).cloned().collect()

branches/try/src/libcollections/enum_set.rs

@@ -428,19 +428,19 @@ mod test {
 
         e1.insert(A);
         let elems: ::vec::Vec<_> = e1.iter().collect();
-        assert_eq!(vec![A], elems);
+        assert_eq!([A], elems);
 
         e1.insert(C);
         let elems: ::vec::Vec<_> = e1.iter().collect();
-        assert_eq!(vec![A,C], elems);
+        assert_eq!([A,C], elems);
 
         e1.insert(C);
         let elems: ::vec::Vec<_> = e1.iter().collect();
-        assert_eq!(vec![A,C], elems);
+        assert_eq!([A,C], elems);
 
         e1.insert(B);
         let elems: ::vec::Vec<_> = e1.iter().collect();
-        assert_eq!(vec![A,B,C], elems);
+        assert_eq!([A,B,C], elems);
     }
 
     ///////////////////////////////////////////////////////////////////////////
@@ -458,35 +458,35 @@ mod test {
 
         let e_union = e1 | e2;
         let elems: ::vec::Vec<_> = e_union.iter().collect();
-        assert_eq!(vec![A,B,C], elems);
+        assert_eq!([A,B,C], elems);
 
         let e_intersection = e1 & e2;
         let elems: ::vec::Vec<_> = e_intersection.iter().collect();
-        assert_eq!(vec![C], elems);
+        assert_eq!([C], elems);
 
         // Another way to express intersection
         let e_intersection = e1 - (e1 - e2);
         let elems: ::vec::Vec<_> = e_intersection.iter().collect();
-        assert_eq!(vec![C], elems);
+        assert_eq!([C], elems);
 
         let e_subtract = e1 - e2;
         let elems: ::vec::Vec<_> = e_subtract.iter().collect();
-        assert_eq!(vec![A], elems);
+        assert_eq!([A], elems);
 
         // Bitwise XOR of two sets, aka symmetric difference
         let e_symmetric_diff = e1 ^ e2;
         let elems: ::vec::Vec<_> = e_symmetric_diff.iter().collect();
-        assert_eq!(vec![A,B], elems);
+        assert_eq!([A,B], elems);
 
         // Another way to express symmetric difference
         let e_symmetric_diff = (e1 - e2) | (e2 - e1);
         let elems: ::vec::Vec<_> = e_symmetric_diff.iter().collect();
-        assert_eq!(vec![A,B], elems);
+        assert_eq!([A,B], elems);
 
         // Yet another way to express symmetric difference
         let e_symmetric_diff = (e1 | e2) - (e1 & e2);
         let elems: ::vec::Vec<_> = e_symmetric_diff.iter().collect();
-        assert_eq!(vec![A,B], elems);
+        assert_eq!([A,B], elems);
     }
 
     #[test]

branches/try/src/libcollections/linked_list.rs

@@ -777,7 +777,7 @@ impl<'a, A> IterMut<'a, A> {
     /// }
     /// {
     ///     let vec: Vec<_> = list.into_iter().collect();
-    ///     assert_eq!(vec, vec![1, 2, 3, 4]);
+    ///     assert_eq!(vec, [1, 2, 3, 4]);
     /// }
     /// ```
     #[inline]
@@ -1273,7 +1273,7 @@ mod tests {
         }
         check_links(&m);
         assert_eq!(m.len(), 3 + len * 2);
-        assert_eq!(m.into_iter().collect::<Vec<_>>(), vec![-2,0,1,2,3,4,5,6,7,8,9,0,1]);
+        assert_eq!(m.into_iter().collect::<Vec<_>>(), [-2,0,1,2,3,4,5,6,7,8,9,0,1]);
     }
 
     #[test]

branches/try/src/libcollections/macros.rs

@@ -26,7 +26,7 @@
 ///
 /// ```
 /// let v = vec![1; 3];
-/// assert_eq!(v, vec![1, 1, 1]);
+/// assert_eq!(v, [1, 1, 1]);
 /// ```
 ///
 /// Note that unlike array expressions this syntax supports all elements