A new `times` method on numeric types

This method is intended to elegantly subsume two common iteration functions.
The first is `iter::range`, which is used identically to the method introduced
in this commit, but currently works only on uints. The second is a common case
of `{int, i8, uint, etc.}::range`, in the case where the inductive variable is
ignored. Compare the usage of the three:
```
for iter::range(100u) {
    // do whatever
}

for int::range(0, 100) |_i| {
    // do whatever
}

for 100.times {
    // do whatever
}
```
I feel that the latter reads much more nicely than the first two approaches,
and unlike the first two the new method allows the user to ignore the specific
type of the number (ineed, if we're throwing away the inductive variable, who
cares what type it is?). A minor benefit is that this new method will be
somewhat familiar to users of Ruby, from which we borrow the name "times".

1 files changed, 25 insertions, 1 deletions

diff --git a/src/libcore/uint-template.rs b/src/libcore/uint-template.rs
index 91b9eb856e4..0433cd7ce30 100644
--- a/src/libcore/uint-template.rs
+++ b/src/libcore/uint-template.rs
@@ -11,7 +11,7 @@ export range;
 export compl;
 export to_str, to_str_bytes;
 export from_str, from_str_radix, str, parse_buf;
-export num, ord, eq;
+export num, ord, eq, times;
 
 const min_value: T = 0 as T;
 const max_value: T = 0 as T - 1 as T;
@@ -104,6 +104,22 @@ fn parse_buf(buf: ~[u8], radix: uint) -> option<T> {
     };
 }
 
+impl times of iter::times for T {
+    #[inline(always)]
+    #[doc = "A convenience form for basic iteration. Given a variable `x` \
+        of any numeric type, the expression `for x.times { /* anything */ }` \
+        will execute the given function exactly x times. If we assume that \
+        `x` is an int, this is functionally equivalent to \
+        `for int::range(0, x) |_i| { /* anything */ }`."]
+    fn times(it: fn() -> bool) {
+        let mut i = self;
+        while i > 0 {
+            if !it() { break }
+            i -= 1;
+        }
+    }
+}
+
 /// Parse a string to an int
 fn from_str(s: str) -> option<T> { parse_buf(str::bytes(s), 10u) }
 
@@ -259,3 +275,11 @@ fn to_str_radix1() {
 fn to_str_radix17() {
     uint::to_str(100u, 17u);
 }
+
+#[test]
+fn test_times() {
+    let ten = 10 as T;
+    let mut accum = 0;
+    for ten.times { accum += 1; }
+    assert (accum == 10);
+}