Use mrb_funcall_id() extensively.

Except for support files e.g. `mruby-test/driver.c`, which are not
target of symbol collection via `rake gensym`.

src/array.c

@@ -1090,7 +1090,7 @@ mrb_ary_splat(mrb_state *mrb, mrb_value v)
     return mrb_ary_new_from_values(mrb, 1, &v);
   }
 
-  ary = mrb_funcall(mrb, v, "to_a", 0);
+  ary = mrb_funcall_id(mrb, v, MRB_SYM(to_a), 0);
   if (mrb_nil_p(ary)) {
     return mrb_ary_new_from_values(mrb, 1, &v);
   }

src/error.c

@@ -114,7 +114,7 @@ exc_to_s(mrb_state *mrb, mrb_value exc)
 static mrb_value
 exc_message(mrb_state *mrb, mrb_value exc)
 {
-  return mrb_funcall(mrb, exc, "to_s", 0);
+  return mrb_funcall_id(mrb, exc, MRB_SYM(to_s), 0);
 }
 
 /*

src/hash.c

@@ -72,7 +72,7 @@ ht_hash_func(mrb_state *mrb, htable *t, mrb_value key)
     break;
 
   default:
-    hv = mrb_funcall(mrb, key, "hash", 0);
+    hv = mrb_funcall_id(mrb, key, MRB_SYM(hash), 0);
     h = (size_t)tt ^ (size_t)mrb_fixnum(hv);
     break;
   }
@@ -856,7 +856,7 @@ hash_default(mrb_state *mrb, mrb_value hash, mrb_value key)
 {
   if (MRB_RHASH_DEFAULT_P(hash)) {
     if (MRB_RHASH_PROCDEFAULT_P(hash)) {
-      return mrb_funcall(mrb, RHASH_PROCDEFAULT(hash), "call", 2, hash, key);
+      return mrb_funcall_id(mrb, RHASH_PROCDEFAULT(hash), MRB_SYM(call), 2, hash, key);
     }
     else {
       return RHASH_IFNONE(hash);
@@ -897,7 +897,7 @@ mrb_hash_default(mrb_state *mrb, mrb_value hash)
   if (MRB_RHASH_DEFAULT_P(hash)) {
     if (MRB_RHASH_PROCDEFAULT_P(hash)) {
       if (!given) return mrb_nil_value();
-      return mrb_funcall(mrb, RHASH_PROCDEFAULT(hash), "call", 2, hash, key);
+      return mrb_funcall_id(mrb, RHASH_PROCDEFAULT(hash), MRB_SYM(call), 2, hash, key);
     }
     else {
       return RHASH_IFNONE(hash);
@@ -1083,7 +1083,7 @@ mrb_hash_shift(mrb_state *mrb, mrb_value hash)
 
   if (MRB_RHASH_DEFAULT_P(hash)) {
     if (MRB_RHASH_PROCDEFAULT_P(hash)) {
-      return mrb_funcall(mrb, RHASH_PROCDEFAULT(hash), "call", 2, hash, mrb_nil_value());
+      return mrb_funcall_id(mrb, RHASH_PROCDEFAULT(hash), MRB_SYM(call), 2, hash, mrb_nil_value());
     }
     else {
       return RHASH_IFNONE(hash);

src/kernel.c

@@ -310,7 +310,7 @@ init_copy(mrb_state *mrb, mrb_value dest, mrb_value obj)
     default:
       break;
   }
-  mrb_funcall(mrb, dest, "initialize_copy", 1, obj);
+  mrb_funcall_id(mrb, dest, MRB_SYM(initialize_copy), 1, obj);
 }
 
 /* 15.3.1.3.8  */
@@ -411,8 +411,8 @@ mrb_obj_extend(mrb_state *mrb, mrb_int argc, mrb_value *argv, mrb_value obj)
     mrb_check_type(mrb, argv[i], MRB_TT_MODULE);
   }
   while (argc--) {
-    mrb_funcall(mrb, argv[argc], "extend_object", 1, obj);
-    mrb_funcall(mrb, argv[argc], "extended", 1, obj);
+    mrb_funcall_id(mrb, argv[argc], MRB_SYM(extend_object), 1, obj);
+    mrb_funcall_id(mrb, argv[argc], MRB_SYM(extended), 1, obj);
   }
   return obj;
 }
@@ -749,7 +749,7 @@ obj_respond_to(mrb_state *mrb, mrb_value self)
   mrb_get_args(mrb, "n|b", &id, &priv);
   respond_to_p = basic_obj_respond_to(mrb, self, id, !priv);
   if (!respond_to_p) {
-    rtm_id = mrb_intern_lit(mrb, "respond_to_missing?");
+    rtm_id = MRB_QSYM(respond_to_missing_p);
     if (basic_obj_respond_to(mrb, self, rtm_id, !priv)) {
       mrb_value args[2], v;
       args[0] = mrb_symbol_value(id);

src/numeric.c

@@ -1558,7 +1558,7 @@ mrb_cmp(mrb_state *mrb, mrb_value obj1, mrb_value obj2)
       return -2;
     return mrb_str_cmp(mrb, obj1, obj2);
   default:
-    v = mrb_funcall(mrb, obj1, "<=>", 1, obj2);
+    v = mrb_funcall_id(mrb, obj1, MRB_SYM(cmp), 1, obj2);
     if (mrb_nil_p(v) || !mrb_fixnum_p(v))
       return -2;
     return mrb_fixnum(v);

src/object.c

@@ -58,7 +58,7 @@ mrb_equal(mrb_state *mrb, mrb_value obj1, mrb_value obj2)
       return TRUE;
   }
 #endif
-  result = mrb_funcall(mrb, obj1, "==", 1, obj2);
+  result = mrb_funcall_id(mrb, obj1, MRB_QSYM(eq), 1, obj2);
   if (mrb_test(result)) return TRUE;
   return FALSE;
 }
@@ -648,12 +648,12 @@ mrb_check_hash_type(mrb_state *mrb, mrb_value hash)
 MRB_API mrb_value
 mrb_inspect(mrb_state *mrb, mrb_value obj)
 {
-  return mrb_obj_as_string(mrb, mrb_funcall(mrb, obj, "inspect", 0));
+  return mrb_obj_as_string(mrb, mrb_funcall_id(mrb, obj, MRB_SYM(inspect), 0));
 }
 
 MRB_API mrb_bool
 mrb_eql(mrb_state *mrb, mrb_value obj1, mrb_value obj2)
 {
   if (mrb_obj_eq(mrb, obj1, obj2)) return TRUE;
-  return mrb_test(mrb_funcall(mrb, obj1, "eql?", 1, obj2));
+  return mrb_test(mrb_funcall_id(mrb, obj1, MRB_QSYM(eql_p), 1, obj2));
 }