Rename last to last_opt, last_unsafe to last

As per discussion on IRC. I am about to file an RFC for further
discussion about the more general issue of whether to enforce
invariants through types, typestate, or dynamic checks, but for now,
removing the misleading name "last_unsafe".

src/libcore/path.rs

@@ -170,7 +170,7 @@ fn splitext(p: path) -> (str, str) {
         if vec::len(parts) > 1u {
             let base = str::connect(vec::init(parts), ".");
             // We just checked that parts is non-empty, so this is safe
-            let ext = "." + vec::last_unsafe(parts);
+            let ext = "." + vec::last(parts);
 
             fn is_dotfile(base: str) -> bool {
                 str::is_empty(base)

src/libcore/vec.rs

@@ -187,27 +187,24 @@ fn init<T: copy>(v: [const T]) -> [T] {
 /*
 Function: last
 
-Returns the last element of a vector
-
-Returns:
+Returns the last element of a `v`, failing if the vector is empty.
 
-An option containing the last element of `v` if `v` is not empty, or
-none if `v` is empty.
 */
-pure fn last<T: copy>(v: [const T]) -> option<T> {
-    if len(v) == 0u { ret none; }
-    ret some(v[len(v) - 1u]);
+pure fn last<T: copy>(v: [const T]) -> T {
+    if len(v) == 0u { fail "last_unsafe: empty vector" }
+    v[len(v) - 1u]
 }
 
 /*
-Function: last_unsafe
+Function: last_opt
 
-Returns the last element of a `v`, failing if the vector is empty.
+Returns some(x) where `x` is the last element of a vector `v`,
+or none if the vector is empty.
 
 */
-pure fn last_unsafe<T: copy>(v: [const T]) -> T {
-    if len(v) == 0u { fail "last_unsafe: empty vector" }
-    v[len(v) - 1u]
+pure fn last_opt<T: copy>(v: [const T]) -> option<T> {
+    if len(v) == 0u { ret none; }
+    some(v[len(v) - 1u])
 }
 
 /*
@@ -1270,11 +1267,11 @@ fn test_tail() {
 
     #[test]
     fn test_last() {
-        let n = last([]);
+        let n = last_opt([]);
         assert (n == none);
-        n = last([1, 2, 3]);
+        n = last_opt([1, 2, 3]);
         assert (n == some(3));
-        n = last([1, 2, 3, 4, 5]);
+        n = last_opt([1, 2, 3, 4, 5]);
         assert (n == some(5));
     }
 

src/libstd/fs.rs

@@ -271,7 +271,7 @@ fn splitext(p: path) -> (str, str) {
         if vec::len(parts) > 1u {
             let base = str::connect(vec::init(parts), ".");
             // We just checked that parts is non-empty
-            let ext = "." + vec::last_unsafe(parts);
+            let ext = "." + vec::last(parts);
 
             fn is_dotfile(base: str) -> bool {
                 str::is_empty(base)

src/rustc/front/attr.rs

@@ -256,7 +256,7 @@ fn meta_item_from_list(
     name: str
 ) -> option<@ast::meta_item> {
     let items = attr::find_meta_items_by_name(items, name);
-    vec::last(items)
+    vec::last_opt(items)
 }
 
 fn meta_item_value_from_list(

src/rustc/metadata/creader.rs

@@ -144,7 +144,7 @@ fn find_library_crate(sess: session::session, ident: ast::ident,
     let crate_name =
         {
             let name_items = attr::find_meta_items_by_name(metas, "name");
-            alt vec::last(name_items) {
+            alt vec::last_opt(name_items) {
               some(i) {
                 alt attr::get_meta_item_value_str(i) {
                   some(n) { n }

src/rustc/middle/ast_map.rs

@@ -189,7 +189,7 @@ fn map_view_item(vi: @view_item, cx: ctx, _v: vt) {
               view_path_glob(pth, id) | view_path_list(pth, _, id) {
                   // should be a constraint on the type
                 assert (vec::is_not_empty(*pth));
-                (id, vec::last_unsafe(*pth))
+                (id, vec::last(*pth))
               }
             };
             cx.map.insert(id, node_export(vp, extend(cx, name)));

src/rustc/middle/pat_util.rs

@@ -70,5 +70,5 @@ fn pat_binding_ids(dm: resolve::def_map, pat: @pat) -> [node_id] {
 
 fn path_to_ident(p: @path) -> ident {
   assert (vec::is_not_empty(p.node.idents)); // should be a constraint on path
-  vec::last_unsafe(p.node.idents)
+  vec::last(p.node.idents)
 }

src/rustc/middle/tstate/bitvectors.rs

@@ -183,7 +183,7 @@ fn kill_poststate(fcx: fn_ctxt, id: node_id, c: tsconstr) -> bool {
 fn clear_in_poststate_expr(fcx: fn_ctxt, e: @expr, t: poststate) {
     alt e.node {
       expr_path(p) {
-        alt vec::last(p.node.idents) {
+        alt vec::last_opt(p.node.idents) {
           some(i) {
             alt local_node_id_to_def(fcx, e.id) {
               some(def_local(nid, _)) {

src/rustc/middle/tstate/states.rs

@@ -406,7 +406,7 @@ fn find_pre_post_state_expr(fcx: fn_ctxt, pres: prestate, e: @expr) -> bool {
                                                     init_assign),
                                       exs, return_val);
 
-        let base_pres = alt vec::last(exs) { none { pres }
+        let base_pres = alt vec::last_opt(exs) { none { pres }
                           some(f) { expr_poststate(fcx.ccx, f) }};
         option::may(maybe_base, {|base|
             changed |= find_pre_post_state_expr(fcx, base_pres, base) |

src/rustc/middle/typeck.rs

@@ -2642,7 +2642,7 @@ fn bind_params(fcx: @fn_ctxt, tp: ty::t, count: uint)
 }
 
 fn get_self_info(ccx: @crate_ctxt) -> option<self_info> {
-    ret vec::last(ccx.self_infos);
+    ret vec::last_opt(ccx.self_infos);
 }
 
 fn check_decl_initializer(fcx: @fn_ctxt, nid: ast::node_id,

src/rustc/util/common.rs

@@ -89,7 +89,9 @@ fn local_rhs_span(l: @ast::local, def: span) -> span {
 }
 
 fn is_main_name(path: middle::ast_map::path) -> bool {
-    option::get(vec::last(path)) == middle::ast_map::path_name("main")
+    // FIXME: path should be a constrained type, so we know
+    // the call to last doesn't fail
+    vec::last(path) == middle::ast_map::path_name("main")
 }
 
 //

src/rustdoc/reexport_pass.rs

@@ -163,7 +163,7 @@ fn build_reexport_path_map(srv: astsrv::srv, -def_map: def_map) -> path_map {
             };
           // should be a constraint on the node_export constructor
           // that guarantees path is non-empty
-            let name = alt check vec::last_unsafe(*path) {
+            let name = alt check vec::last(*path) {
               ast_map::path_name(nm) { nm }
             };
             let modpath = ast_map::path_to_str(vec::init(*path));

src/test/run-pass/zip-same-length.rs

@@ -19,5 +19,5 @@ fn main() {
 
     check (is_not_empty(ps));
     assert (head(ps) == ('a', 1u));
-    assert (last_unsafe(ps) == (j as char, 10u));
+    assert (last(ps) == (j as char, 10u));
 }