Patch to allow Ruby's Array#map to take a symbol.

benchmark output

$ ./ruby -I. -Ilib/ -w map_symbol_bench.rb 
Rehearsal --------------------------------------------
nil        0.050000   0.000000   0.050000 (  0.046891)
identity   0.880000   0.000000   0.880000 (  0.887874)
block      1.080000   0.000000   1.080000 (  1.078556)
to_proc    0.990000   0.000000   0.990000 (  0.996956)
----------------------------------- total: 3.000000sec

               user     system      total        real
nil        0.040000   0.000000   0.040000 (  0.045237)
identity   0.860000   0.000000   0.860000 (  0.866740)
block      1.070000   0.000000   1.070000 (  1.066750)
to_proc    0.990000   0.000000   0.990000 (  0.986012)

benchmark.rb

require 'benchmark'
a = (0..10).to_a
n = ARGV.first || 1_000_000

Benchmark.bmbm do |b|
  b.report("nil") { n.times { nil } }
  b.report("identity") { n.times { a.map {|i| i } } }
  b.report("block") { n.times { a.map {|i| i.to_i } } }
  b.report("to_proc") { n.times { a.map(&:to_i) } }
  b.report("symbol") { n.times { a.map(:to_i) } }
end

ruby_symbol_map.diff

diff --git a/array.c b/array.c
index 76a3a62..7cdd041 100644
--- a/array.c
+++ b/array.c
@@ -2530,16 +2530,29 @@ rb_ary_sort_by_bang(VALUE ary)
  */
 
 static VALUE
-rb_ary_collect(VALUE ary)
+rb_ary_collect(int argc, VALUE *argv, VALUE ary)
 {
     long i;
-    VALUE collect;
+    VALUE collect, op;
+    ID id;
 
-    RETURN_SIZED_ENUMERATOR(ary, 0, 0, rb_ary_length);
     collect = rb_ary_new2(RARRAY_LEN(ary));
-    for (i = 0; i < RARRAY_LEN(ary); i++) {
-	rb_ary_push(collect, rb_yield(RARRAY_PTR(ary)[i]));
+
+    if (rb_scan_args(argc, argv, "01", &op) > 0) {
+      id = rb_check_id(&op);
+
+      for (i = 0; i < RARRAY_LEN(ary); i++) {
+        rb_ary_push(collect, rb_funcall(RARRAY_PTR(ary)[i], id, 0));
+      }
     }
+    else {
+      RETURN_SIZED_ENUMERATOR(ary, 0, 0, rb_ary_length);
+
+      for (i = 0; i < RARRAY_LEN(ary); i++) {
+        rb_ary_push(collect, rb_yield(RARRAY_PTR(ary)[i]));
+      }
+    }
+
     return collect;
 }
 
@@ -5493,9 +5506,9 @@ Init_Array(void)
     rb_define_method(rb_cArray, "sort", rb_ary_sort, 0);
     rb_define_method(rb_cArray, "sort!", rb_ary_sort_bang, 0);
     rb_define_method(rb_cArray, "sort_by!", rb_ary_sort_by_bang, 0);
-    rb_define_method(rb_cArray, "collect", rb_ary_collect, 0);
+    rb_define_method(rb_cArray, "collect", rb_ary_collect, -1);
     rb_define_method(rb_cArray, "collect!", rb_ary_collect_bang, 0);
-    rb_define_method(rb_cArray, "map", rb_ary_collect, 0);
+    rb_define_method(rb_cArray, "map", rb_ary_collect, -1);
     rb_define_method(rb_cArray, "map!", rb_ary_collect_bang, 0);
     rb_define_method(rb_cArray, "select", rb_ary_select, 0);
     rb_define_method(rb_cArray, "select!", rb_ary_select_bang, 0);