stdlib: Sketch out ivec::init_fn, currently segfaulting

Author: pcwalton

src/lib/ivec.rs

@@ -33,6 +33,16 @@ fn len[T](&T[] v) -> uint {
     ret rusti::ivec_len(v);
 }
 
+type init_op[T] = fn(uint) -> T;
+
+fn init_fn[T](&init_op[T] op, uint n_elts) -> T[] {
+    auto v = ~[];
+    reserve(v, n_elts);
+    let uint i = 0u;
+    while (i < n_elts) { v += ~[op(i)]; i += 1u; }
+    ret v;
+}
+
 mod unsafe {
     fn copy_from_buf[T](&mutable T[] v, *T ptr, uint count) {
         ret rustrt::ivec_copy_from_buf(v, ptr, count);

src/test/run-pass/lib-ivec.rs

@@ -34,8 +34,18 @@ fn test_unsafe_ptrs() {
     assert (d.(4) == 5);
 }
 
+fn test_init_fn() {
+    fn square(uint n) -> uint { ret n * n; }
+    auto v = ivec::init_fn(square, 3u);
+    assert (ivec::len(v) == 3u);
+    assert (v.(0) == 1u);
+    assert (v.(1) == 4u);
+    assert (v.(2) == 9u);
+}
+
 fn main() {
     test_reserve_and_on_heap();
     //test_unsafe_ptrs();
+    //test_init_fn();
 }