Add `mrb_get_arg1()` that retrieves single (and only) argument.

`mrb_get_arg1()` raises `ArgumentError` if the method does not receive one
argument.

And replaces all `mrb_get_args(mrb, "o", &arg)` by the new function.

25 files changed, 130 insertions, 209 deletions

diff --git a/include/mruby.h b/include/mruby.h
index fef4a0d47..5aba2934a 100644
--- a/include/mruby.h
+++ b/include/mruby.h
@@ -959,8 +959,21 @@ mrb_get_mid(mrb_state *mrb) /* get method symbol */
  */
 MRB_API mrb_int mrb_get_argc(mrb_state *mrb);
 
+/**
+ * Retrieve an array of arguments from mrb_state.
+ *
+ * Correctly handles *splat arguments.
+ */
 MRB_API mrb_value* mrb_get_argv(mrb_state *mrb);
 
+/**
+ * Retrieve the first and only argument from mrb_state.
+ * Raises ArgumentError unless the number of arguments is exactly one.
+ *
+ * Correctly handles *splat arguments.
+ */
+MRB_API mrb_value mrb_get_arg1(mrb_state *mrb);
+
 /* `strlen` for character string literals (use with caution or `strlen` instead)
     Adjacent string literals are concatenated in C/C++ in translation phase 6.
     If `lit` is not one, the compiler will report a syntax error:
diff --git a/mrbgems/mruby-array-ext/src/array.c b/mrbgems/mruby-array-ext/src/array.c
index ab6d99133..0cb61b2ab 100644
--- a/mrbgems/mruby-array-ext/src/array.c
+++ b/mrbgems/mruby-array-ext/src/array.c
@@ -28,9 +28,8 @@ static mrb_value
 mrb_ary_assoc(mrb_state *mrb, mrb_value ary)
 {
   mrb_int i;
-  mrb_value v, k;
-
-  mrb_get_args(mrb, "o", &k);
+  mrb_value v;
+  mrb_value k = mrb_get_arg1(mrb);
 
   for (i = 0; i < RARRAY_LEN(ary); ++i) {
     v = mrb_check_array_type(mrb, RARRAY_PTR(ary)[i]);
@@ -59,9 +58,8 @@ static mrb_value
 mrb_ary_rassoc(mrb_state *mrb, mrb_value ary)
 {
   mrb_int i;
-  mrb_value v, value;
-
-  mrb_get_args(mrb, "o", &value);
+  mrb_value v;
+  mrb_value value = mrb_get_arg1(mrb);
 
   for (i = 0; i < RARRAY_LEN(ary); ++i) {
     v = RARRAY_PTR(ary)[i];
diff --git a/mrbgems/mruby-complex/src/complex.c b/mrbgems/mruby-complex/src/complex.c
index 10fa42a2c..0432da633 100644
--- a/mrbgems/mruby-complex/src/complex.c
+++ b/mrbgems/mruby-complex/src/complex.c
@@ -174,7 +174,7 @@ div_pair(struct float_pair *q, struct float_pair const *a,
 static mrb_value
 complex_div(mrb_state *mrb, mrb_value self)
 {
-  mrb_value rhs;
+  mrb_value rhs = mrb_get_arg1(mrb);
   struct mrb_complex *a, *b;
   struct float_pair ar, ai, br, bi;
   struct float_pair br2, bi2;
@@ -183,7 +183,6 @@ complex_div(mrb_state *mrb, mrb_value self)
   struct float_pair ai_br, ar_bi;
   struct float_pair zr, zi;
 
-  mrb_get_args(mrb, "o", &rhs);
   a = complex_ptr(mrb, self);
   b = complex_ptr(mrb, rhs);
 
diff --git a/mrbgems/mruby-fiber/src/fiber.c b/mrbgems/mruby-fiber/src/fiber.c
index 3c17b59dd..00ee7c223 100644
--- a/mrbgems/mruby-fiber/src/fiber.c
+++ b/mrbgems/mruby-fiber/src/fiber.c
@@ -291,8 +291,7 @@ mrb_fiber_alive_p(mrb_state *mrb, mrb_value self)
 static mrb_value
 fiber_eq(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
-  mrb_get_args(mrb, "o", &other);
+  mrb_value other = mrb_get_arg1(mrb);
 
   if (!mrb_fiber_p(other)) {
     return mrb_false_value();
diff --git a/mrbgems/mruby-inline-struct/test/inline.c b/mrbgems/mruby-inline-struct/test/inline.c
index 51804ae31..5d307dcab 100644
--- a/mrbgems/mruby-inline-struct/test/inline.c
+++ b/mrbgems/mruby-inline-struct/test/inline.c
@@ -8,8 +8,7 @@ istruct_test_initialize(mrb_state *mrb, mrb_value self)
 {
   char *string = (char*)mrb_istruct_ptr(self);
   mrb_int size = mrb_istruct_size();
-  mrb_value object;
-  mrb_get_args(mrb, "o", &object);
+  mrb_value object = mrb_get_arg1(mrb);
 
   if (mrb_fixnum_p(object)) {
     strncpy(string, "fixnum", size-1);
@@ -45,8 +44,8 @@ istruct_test_length(mrb_state *mrb, mrb_value self)
 static mrb_value
 istruct_test_test_receive(mrb_state *mrb, mrb_value self)
 {
-  mrb_value object;
-  mrb_get_args(mrb, "o", &object);
+  mrb_value object = mrb_get_arg1(mrb);
+
   if (mrb_obj_class(mrb, object) != mrb_class_get(mrb, "InlineStructTest"))
   {
     mrb_raise(mrb, E_TYPE_ERROR, "Expected InlineStructTest");
diff --git a/mrbgems/mruby-io/src/file.c b/mrbgems/mruby-io/src/file.c
index dd65e2da9..6c99300d8 100644
--- a/mrbgems/mruby-io/src/file.c
+++ b/mrbgems/mruby-io/src/file.c
@@ -492,10 +492,9 @@ mrb_file_truncate(mrb_state *mrb, mrb_value self)
 {
   int fd;
   mrb_int length;
-  mrb_value lenv;
+  mrb_value lenv = mrb_get_arg1(mrb);
 
   fd = mrb_io_fileno(mrb, self);
-  mrb_get_args(mrb, "o", &lenv);
   length = mrb_int(mrb, lenv);
   if (mrb_ftruncate(fd, length) != 0) {
     mrb_raise(mrb, E_IO_ERROR, "ftruncate failed");
diff --git a/mrbgems/mruby-io/src/file_test.c b/mrbgems/mruby-io/src/file_test.c
index 19fd5739b..b7a28f4d3 100644
--- a/mrbgems/mruby-io/src/file_test.c
+++ b/mrbgems/mruby-io/src/file_test.c
@@ -93,9 +93,7 @@ mrb_filetest_s_directory_p(mrb_state *mrb, mrb_value klass)
 #endif
 
   struct stat st;
-  mrb_value obj;
-
-  mrb_get_args(mrb, "o", &obj);
+  mrb_value obj = mrb_get_arg1(mrb);
 
   if (mrb_stat(mrb, obj, &st) < 0)
     return mrb_false_value();
@@ -124,9 +122,7 @@ mrb_filetest_s_pipe_p(mrb_state *mrb, mrb_value klass)
 #  endif
 
   struct stat st;
-  mrb_value obj;
-
-  mrb_get_args(mrb, "o", &obj);
+  mrb_value obj = mrb_get_arg1(mrb);
 
   if (mrb_stat(mrb, obj, &st) < 0)
     return mrb_false_value();
@@ -167,9 +163,7 @@ mrb_filetest_s_symlink_p(mrb_state *mrb, mrb_value klass)
 
 #ifdef S_ISLNK
   struct stat st;
-  mrb_value obj;
-
-  mrb_get_args(mrb, "o", &obj);
+  mrb_value obj = mrb_get_arg1(mrb);
 
   if (mrb_lstat(mrb, obj, &st) == -1)
     return mrb_false_value();
@@ -210,9 +204,7 @@ mrb_filetest_s_socket_p(mrb_state *mrb, mrb_value klass)
 
 #ifdef S_ISSOCK
   struct stat st;
-  mrb_value obj;
-
-  mrb_get_args(mrb, "o", &obj);
+  mrb_value obj = mrb_get_arg1(mrb);
 
   if (mrb_stat(mrb, obj, &st) < 0)
     return mrb_false_value();
@@ -236,9 +228,8 @@ static mrb_value
 mrb_filetest_s_exist_p(mrb_state *mrb, mrb_value klass)
 {
   struct stat st;
-  mrb_value obj;
+  mrb_value obj = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &obj);
   if (mrb_stat(mrb, obj, &st) < 0)
     return mrb_false_value();
 
@@ -261,9 +252,7 @@ mrb_filetest_s_file_p(mrb_state *mrb, mrb_value klass)
 #endif
 
   struct stat st;
-  mrb_value obj;
-
-  mrb_get_args(mrb, "o", &obj);
+  mrb_value obj = mrb_get_arg1(mrb);
 
   if (mrb_stat(mrb, obj, &st) < 0)
     return mrb_false_value();
@@ -285,9 +274,7 @@ static mrb_value
 mrb_filetest_s_zero_p(mrb_state *mrb, mrb_value klass)
 {
   struct stat st;
-  mrb_value obj;
-
-  mrb_get_args(mrb, "o", &obj);
+  mrb_value obj = mrb_get_arg1(mrb);
 
   if (mrb_stat(mrb, obj, &st) < 0)
     return mrb_false_value();
@@ -310,9 +297,7 @@ static mrb_value
 mrb_filetest_s_size(mrb_state *mrb, mrb_value klass)
 {
   struct stat st;
-  mrb_value obj;
-
-  mrb_get_args(mrb, "o", &obj);
+  mrb_value obj = mrb_get_arg1(mrb);
 
   if (mrb_stat(mrb, obj, &st) < 0)
     mrb_sys_fail(mrb, "mrb_stat");
@@ -332,9 +317,7 @@ static mrb_value
 mrb_filetest_s_size_p(mrb_state *mrb, mrb_value klass)
 {
   struct stat st;
-  mrb_value obj;
-
-  mrb_get_args(mrb, "o", &obj);
+  mrb_value obj = mrb_get_arg1(mrb);
 
   if (mrb_stat(mrb, obj, &st) < 0)
     return mrb_nil_value();
diff --git a/mrbgems/mruby-io/src/io.c b/mrbgems/mruby-io/src/io.c
index ef1283b51..505ceb248 100644
--- a/mrbgems/mruby-io/src/io.c
+++ b/mrbgems/mruby-io/src/io.c
@@ -599,13 +599,12 @@ mrb_dup(mrb_state *mrb, int fd, mrb_bool *failed)
 static mrb_value
 mrb_io_initialize_copy(mrb_state *mrb, mrb_value copy)
 {
-  mrb_value orig;
+  mrb_value orig = mrb_get_arg1(mrb);
   mrb_value buf;
   struct mrb_io *fptr_copy;
   struct mrb_io *fptr_orig;
   mrb_bool failed = TRUE;
 
-  mrb_get_args(mrb, "o", &orig);
   fptr_orig = io_get_open_fptr(mrb, orig);
   fptr_copy = (struct mrb_io *)DATA_PTR(copy);
   if (fptr_orig == fptr_copy) return copy;
diff --git a/mrbgems/mruby-kernel-ext/src/kernel.c b/mrbgems/mruby-kernel-ext/src/kernel.c
index 427740c1c..1d183aecd 100644
--- a/mrbgems/mruby-kernel-ext/src/kernel.c
+++ b/mrbgems/mruby-kernel-ext/src/kernel.c
@@ -128,9 +128,8 @@ mrb_f_integer(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_f_float(mrb_state *mrb, mrb_value self)
 {
-  mrb_value arg;
+  mrb_value arg = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &arg);
   return mrb_Float(mrb, arg);
 }
 #endif
@@ -149,9 +148,9 @@ mrb_f_float(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_f_string(mrb_state *mrb, mrb_value self)
 {
-  mrb_value arg, tmp;
+  mrb_value arg = mrb_get_arg1(mrb);
+  mrb_value tmp;
 
-  mrb_get_args(mrb, "o", &arg);
   tmp = mrb_convert_type(mrb, arg, MRB_TT_STRING, "String", "to_s");
   return tmp;
 }
@@ -168,9 +167,9 @@ mrb_f_string(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_f_array(mrb_state *mrb, mrb_value self)
 {
-  mrb_value arg, tmp;
+  mrb_value arg = mrb_get_arg1(mrb);
+  mrb_value tmp;
 
-  mrb_get_args(mrb, "o", &arg);
   tmp = mrb_check_convert_type(mrb, arg, MRB_TT_ARRAY, "Array", "to_a");
   if (mrb_nil_p(tmp)) {
     return mrb_ary_new_from_values(mrb, 1, &arg);
@@ -196,9 +195,8 @@ mrb_f_array(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_f_hash(mrb_state *mrb, mrb_value self)
 {
-  mrb_value arg;
+  mrb_value arg = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &arg);
   if (mrb_nil_p(arg) || (mrb_array_p(arg) && RARRAY_LEN(arg) == 0)) {
     return mrb_hash_new(mrb);
   }
diff --git a/mrbgems/mruby-method/src/method.c b/mrbgems/mruby-method/src/method.c
index d249b463b..111b031b9 100644
--- a/mrbgems/mruby-method/src/method.c
+++ b/mrbgems/mruby-method/src/method.c
@@ -33,9 +33,8 @@ unbound_method_bind(mrb_state *mrb, mrb_value self)
   mrb_value name = mrb_iv_get(mrb, self, mrb_intern_lit(mrb, "_name"));
   mrb_value proc = mrb_iv_get(mrb, self, mrb_intern_lit(mrb, "_proc"));
   mrb_value klass = mrb_iv_get(mrb, self, mrb_intern_lit(mrb, "_klass"));
-  mrb_value recv;
+  mrb_value recv = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &recv);
   bind_check(mrb, recv, owner);
   me = method_object_alloc(mrb, mrb_class_get(mrb, "Method"));
   mrb_obj_iv_set(mrb, me, mrb_intern_lit(mrb, "_owner"), owner);
@@ -51,11 +50,11 @@ unbound_method_bind(mrb_state *mrb, mrb_value self)
 static mrb_value
 method_eql(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other, receiver, orig_proc, other_proc;
+  mrb_value other = mrb_get_arg1(mrb);
+  mrb_value receiver, orig_proc, other_proc;
   struct RClass *owner, *klass;
   struct RProc *orig_rproc, *other_rproc;
 
-  mrb_get_args(mrb, "o", &other);
   if (!mrb_obj_is_instance_of(mrb, other, mrb_class(mrb, self)))
     return mrb_false_value();
 
diff --git a/mrbgems/mruby-print/src/print.c b/mrbgems/mruby-print/src/print.c
index 66d070f60..9301dbe55 100644
--- a/mrbgems/mruby-print/src/print.c
+++ b/mrbgems/mruby-print/src/print.c
@@ -45,9 +45,8 @@ printstr(mrb_state *mrb, mrb_value obj)
 mrb_value
 mrb_printstr(mrb_state *mrb, mrb_value self)
 {
-  mrb_value argv;
+  mrb_value argv = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &argv);
   printstr(mrb, argv);
 
   return argv;
diff --git a/mrbgems/mruby-range-ext/src/range.c b/mrbgems/mruby-range-ext/src/range.c
index 36b684fad..2a0b4e97d 100644
--- a/mrbgems/mruby-range-ext/src/range.c
+++ b/mrbgems/mruby-range-ext/src/range.c
@@ -34,12 +34,10 @@ r_lt(mrb_state *mrb, mrb_value a, mrb_value b)
 static mrb_value
 range_cover(mrb_state *mrb, mrb_value range)
 {
-  mrb_value val;
   struct RRange *r = mrb_range_ptr(mrb, range);
+  mrb_value val = mrb_get_arg1(mrb);
   mrb_value beg, end;
 
-  mrb_get_args(mrb, "o", &val);
-
   beg = RANGE_BEG(r);
   end = RANGE_END(r);
 
diff --git a/mrbgems/mruby-string-ext/src/string.c b/mrbgems/mruby-string-ext/src/string.c
index ea9508be0..7cf146ec8 100644
--- a/mrbgems/mruby-string-ext/src/string.c
+++ b/mrbgems/mruby-string-ext/src/string.c
@@ -164,9 +164,8 @@ mrb_str_swapcase(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_str_concat_m(mrb_state *mrb, mrb_value self)
 {
-  mrb_value str;
+  mrb_value str = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &str);
   if (mrb_fixnum_p(str) || mrb_float_p(str))
 #ifdef MRB_UTF8_STRING
     str = int_chr_utf8(mrb, str);
diff --git a/mrbgems/mruby-struct/src/struct.c b/mrbgems/mruby-struct/src/struct.c
index f42a5f1ea..7fbf9225f 100644
--- a/mrbgems/mruby-struct/src/struct.c
+++ b/mrbgems/mruby-struct/src/struct.c
@@ -154,9 +154,8 @@ mrb_struct_set_m(mrb_state *mrb, mrb_value obj)
 {
   mrb_int i = mrb_fixnum(mrb_proc_cfunc_env_get(mrb, 0));
   mrb_value *ptr;
-  mrb_value val;
+  mrb_value val = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &val);
   mrb_struct_modify(mrb, obj);
   ptr = RSTRUCT_PTR(obj);
   if (ptr == NULL || i >= RSTRUCT_LEN(obj)) {
@@ -356,9 +355,7 @@ mrb_struct_initialize(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_struct_init_copy(mrb_state *mrb, mrb_value copy)
 {
-  mrb_value s;
-
-  mrb_get_args(mrb, "o", &s);
+  mrb_value s = mrb_get_arg1(mrb);
 
   if (mrb_obj_equal(mrb, copy, s)) return copy;
   if (!mrb_obj_is_instance_of(mrb, s, mrb_obj_class(mrb, copy))) {
@@ -428,9 +425,8 @@ struct_aref_int(mrb_state *mrb, mrb_value s, mrb_int i)
 static mrb_value
 mrb_struct_aref(mrb_state *mrb, mrb_value s)
 {
-  mrb_value idx;
+  mrb_value idx = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &idx);
   if (mrb_string_p(idx)) {
     mrb_value sym = mrb_check_intern_str(mrb, idx);
 
@@ -545,11 +541,10 @@ mrb_struct_aset(mrb_state *mrb, mrb_value s)
 static mrb_value
 mrb_struct_equal(mrb_state *mrb, mrb_value s)
 {
-  mrb_value s2;
+  mrb_value s2 = mrb_get_arg1(mrb);
   mrb_value *ptr, *ptr2;
   mrb_int i, len;
 
-  mrb_get_args(mrb, "o", &s2);
   if (mrb_obj_equal(mrb, s, s2)) {
     return mrb_true_value();
   }
@@ -582,11 +577,10 @@ mrb_struct_equal(mrb_state *mrb, mrb_value s)
 static mrb_value
 mrb_struct_eql(mrb_state *mrb, mrb_value s)
 {
-  mrb_value s2;
+  mrb_value s2 = mrb_get_arg1(mrb);
   mrb_value *ptr, *ptr2;
   mrb_int i, len;
 
-  mrb_get_args(mrb, "o", &s2);
   if (mrb_obj_equal(mrb, s, s2)) {
     return mrb_true_value();
   }
diff --git a/mrbgems/mruby-time/src/time.c b/mrbgems/mruby-time/src/time.c
index e76e11649..5fa700848 100644
--- a/mrbgems/mruby-time/src/time.c
+++ b/mrbgems/mruby-time/src/time.c
@@ -515,11 +515,10 @@ time_get_ptr(mrb_state *mrb, mrb_value time)
 static mrb_value
 mrb_time_eq(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
   struct mrb_time *tm1, *tm2;
   mrb_bool eq_p;
 
-  mrb_get_args(mrb, "o", &other);
   tm1 = DATA_GET_PTR(mrb, self, &mrb_time_type, struct mrb_time);
   tm2 = DATA_CHECK_GET_PTR(mrb, other, &mrb_time_type, struct mrb_time);
   eq_p = tm1 && tm2 && tm1->sec == tm2->sec && tm1->usec == tm2->usec;
@@ -530,10 +529,9 @@ mrb_time_eq(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_time_cmp(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
   struct mrb_time *tm1, *tm2;
 
-  mrb_get_args(mrb, "o", &other);
   tm1 = DATA_GET_PTR(mrb, self, &mrb_time_type, struct mrb_time);
   tm2 = DATA_CHECK_GET_PTR(mrb, other, &mrb_time_type, struct mrb_time);
   if (!tm1 || !tm2) return mrb_nil_value();
@@ -556,11 +554,10 @@ mrb_time_cmp(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_time_plus(mrb_state *mrb, mrb_value self)
 {
-  mrb_value o;
+  mrb_value o = mrb_get_arg1(mrb);
   struct mrb_time *tm;
   time_t sec, usec;
 
-  mrb_get_args(mrb, "o", &o);
   tm = time_get_ptr(mrb, self);
   sec = mrb_to_time_t(mrb, o, &usec);
   return mrb_time_make_time(mrb, mrb_obj_class(mrb, self), tm->sec+sec, tm->usec+usec, tm->timezone);
@@ -569,10 +566,9 @@ mrb_time_plus(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_time_minus(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
   struct mrb_time *tm, *tm2;
 
-  mrb_get_args(mrb, "o", &other);
   tm = time_get_ptr(mrb, self);
   tm2 = DATA_CHECK_GET_PTR(mrb, other, &mrb_time_type, struct mrb_time);
   if (tm2) {
@@ -770,10 +766,9 @@ mrb_time_initialize(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_time_initialize_copy(mrb_state *mrb, mrb_value copy)
 {
-  mrb_value src;
+  mrb_value src = mrb_get_arg1(mrb);
   struct mrb_time *t1, *t2;
 
-  mrb_get_args(mrb, "o", &src);
   if (mrb_obj_equal(mrb, copy, src)) return copy;
   if (!mrb_obj_is_instance_of(mrb, src, mrb_obj_class(mrb, copy))) {
     mrb_raise(mrb, E_TYPE_ERROR, "wrong argument class");
diff --git a/src/array.c b/src/array.c
index ad0d5b8db..414ccd60a 100644
--- a/src/array.c
+++ b/src/array.c
@@ -1038,10 +1038,9 @@ mrb_ary_last(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_ary_index_m(mrb_state *mrb, mrb_value self)
 {
-  mrb_value obj;
+  mrb_value obj = mrb_get_arg1(mrb);
   mrb_int i;
 
-  mrb_get_args(mrb, "o", &obj);
   for (i = 0; i < RARRAY_LEN(self); i++) {
     if (mrb_equal(mrb, RARRAY_PTR(self)[i], obj)) {
       return mrb_fixnum_value(i);
@@ -1053,10 +1052,9 @@ mrb_ary_index_m(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_ary_rindex_m(mrb_state *mrb, mrb_value self)
 {
-  mrb_value obj;
+  mrb_value obj = mrb_get_arg1(mrb);
   mrb_int i, len;
 
-  mrb_get_args(mrb, "o", &obj);
   for (i = RARRAY_LEN(self) - 1; i >= 0; i--) {
     if (mrb_equal(mrb, RARRAY_PTR(self)[i], obj)) {
       return mrb_fixnum_value(i);
@@ -1230,9 +1228,8 @@ mrb_ary_join_m(mrb_state *mrb, mrb_value ary)
 static mrb_value
 mrb_ary_eq(mrb_state *mrb, mrb_value ary1)
 {
-  mrb_value ary2;
+  mrb_value ary2 = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &ary2);
   if (mrb_obj_equal(mrb, ary1, ary2)) return mrb_true_value();
   if (!mrb_array_p(ary2)) {
     return mrb_false_value();
@@ -1245,9 +1242,8 @@ mrb_ary_eq(mrb_state *mrb, mrb_value ary1)
 static mrb_value
 mrb_ary_cmp(mrb_state *mrb, mrb_value ary1)
 {
-  mrb_value ary2;
+  mrb_value ary2 = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &ary2);
   if (mrb_obj_equal(mrb, ary1, ary2)) return mrb_fixnum_value(0);
   if (!mrb_array_p(ary2)) {
     return mrb_nil_value();
diff --git a/src/class.c b/src/class.c
index d30edd41e..313bf586a 100644
--- a/src/class.c
+++ b/src/class.c
@@ -549,6 +549,23 @@ mrb_get_argv(mrb_state *mrb)
   return array_argv;
 }
 
+MRB_API mrb_value
+mrb_get_arg1(mrb_state *mrb)
+{
+  mrb_int argc = mrb->c->ci->argc;
+  mrb_value *array_argv = mrb->c->stack + 1;
+  if (argc < 0) {
+    struct RArray *a = mrb_ary_ptr(*array_argv);
+
+    argc = ARY_LEN(a);
+    array_argv = ARY_PTR(a);
+  }
+  if (argc != 1) {
+    mrb_raise(mrb, E_ARGUMENT_ERROR, "wrong number of arguments");
+  }
+  return array_argv[0];
+}
+
 void mrb_hash_check_kdict(mrb_state *mrb, mrb_value self);
 
 /*
@@ -1212,10 +1229,9 @@ mrb_mod_ancestors(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_mod_extend_object(mrb_state *mrb, mrb_value mod)
 {
-  mrb_value obj;
+  mrb_value obj = mrb_get_arg1(mrb);
 
   mrb_check_type(mrb, mod, MRB_TT_MODULE);
-  mrb_get_args(mrb, "o", &obj);
   mrb_include_module(mrb, mrb_class_ptr(mrb_singleton_class(mrb, obj)), mrb_class_ptr(mod));
   return mod;
 }
@@ -1493,9 +1509,8 @@ static mrb_value
 attr_writer(mrb_state *mrb, mrb_value obj)
 {
   mrb_value name = mrb_proc_cfunc_env_get(mrb, 0);
-  mrb_value val;
+  mrb_value val = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &val);
   mrb_iv_set(mrb, obj, to_sym(mrb, name), val);
   return val;
 }
@@ -1663,18 +1678,16 @@ mrb_bob_not(mrb_state *mrb, mrb_value cv)
 mrb_value
 mrb_obj_equal_m(mrb_state *mrb, mrb_value self)
 {
-  mrb_value arg;
+  mrb_value arg = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &arg);
   return mrb_bool_value(mrb_obj_equal(mrb, self, arg));
 }
 
 static mrb_value
 mrb_obj_not_equal_m(mrb_state *mrb, mrb_value self)
 {
-  mrb_value arg;
+  mrb_value arg = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &arg);
   return mrb_bool_value(!mrb_equal(mrb, self, arg));
 }
 
@@ -1975,13 +1988,11 @@ mrb_const_get_sym(mrb_state *mrb, mrb_value mod, mrb_sym id)
 static mrb_value
 mrb_mod_const_get(mrb_state *mrb, mrb_value mod)
 {
-  mrb_value path;
+  mrb_value path = mrb_get_arg1(mrb);
   mrb_sym id;
   char *ptr;
   mrb_int off, end, len;
 
-  mrb_get_args(mrb, "o", &path);
-
   if (mrb_symbol_p(path)) {
     /* const get with symbol */
     id = mrb_symbol(path);
@@ -2134,10 +2145,9 @@ top_define_method(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_mod_eqq(mrb_state *mrb, mrb_value mod)
 {
-  mrb_value obj;
+  mrb_value obj = mrb_get_arg1(mrb);
   mrb_bool eqq;
 
-  mrb_get_args(mrb, "o", &obj);
   eqq = mrb_obj_is_kind_of(mrb, obj, mrb_class_ptr(mod));
 
   return mrb_bool_value(eqq);
diff --git a/src/error.c b/src/error.c
index d1bd52d41..5d17209e5 100644
--- a/src/error.c
+++ b/src/error.c
@@ -160,9 +160,8 @@ set_backtrace(mrb_state *mrb, mrb_value exc, mrb_value backtrace)
 static mrb_value
 exc_set_backtrace(mrb_state *mrb, mrb_value exc)
 {
-  mrb_value backtrace;
+  mrb_value backtrace = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &backtrace);
   set_backtrace(mrb, exc, backtrace);
   return backtrace;
 }
diff --git a/src/hash.c b/src/hash.c
index 575d35d12..4d5310903 100644
--- a/src/hash.c
+++ b/src/hash.c
@@ -641,12 +641,11 @@ static mrb_value hash_default(mrb_state *mrb, mrb_value hash, mrb_value key);
 static mrb_value
 mrb_hash_init_copy(mrb_state *mrb, mrb_value self)
 {
-  mrb_value orig;
+  mrb_value orig = mrb_get_arg1(mrb);
   struct RHash* copy;
   htable *orig_h;
   mrb_value ifnone, vret;
 
-  mrb_get_args(mrb, "o", &orig);
   if (mrb_obj_equal(mrb, self, orig)) return self;
   if ((mrb_type(self) != mrb_type(orig)) || (mrb_obj_class(mrb, self) != mrb_obj_class(mrb, orig))) {
       mrb_raise(mrb, E_TYPE_ERROR, "initialize_copy should take same class object");
@@ -828,9 +827,8 @@ mrb_hash_init(mrb_state *mrb, mrb_value hash)
 static mrb_value
 mrb_hash_aget(mrb_state *mrb, mrb_value self)
 {
-  mrb_value key;
+  mrb_value key = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &key);
   return mrb_hash_get(mrb, self, key);
 }
 
@@ -913,9 +911,8 @@ mrb_hash_default(mrb_state *mrb, mrb_value hash)
 static mrb_value
 mrb_hash_set_default(mrb_state *mrb, mrb_value hash)
 {
-  mrb_value ifnone;
+  mrb_value ifnone = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &ifnone);
   mrb_hash_modify(mrb, hash);
   mrb_iv_set(mrb, hash, mrb_intern_lit(mrb, "ifnone"), ifnone);
   RHASH(hash)->flags &= ~MRB_HASH_PROC_DEFAULT;
@@ -969,9 +966,8 @@ mrb_hash_default_proc(mrb_state *mrb, mrb_value hash)
 static mrb_value
 mrb_hash_set_default_proc(mrb_state *mrb, mrb_value hash)
 {
-  mrb_value ifnone;
+  mrb_value ifnone = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &ifnone);
   mrb_hash_modify(mrb, hash);
   mrb_iv_set(mrb, hash, mrb_intern_lit(mrb, "ifnone"), ifnone);
   if (!mrb_nil_p(ifnone)) {
@@ -1003,9 +999,8 @@ mrb_hash_delete_key(mrb_state *mrb, mrb_value hash, mrb_value key)
 static mrb_value
 mrb_hash_delete(mrb_state *mrb, mrb_value self)
 {
-  mrb_value key;
+  mrb_value key = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &key);
   mrb_hash_modify(mrb, self);
   return mrb_hash_delete_key(mrb, self, key);
 }
@@ -1288,10 +1283,9 @@ mrb_hash_key_p(mrb_state *mrb, mrb_value hash, mrb_value key)
 static mrb_value
 mrb_hash_has_key(mrb_state *mrb, mrb_value hash)
 {
-  mrb_value key;
+  mrb_value key = mrb_get_arg1(mrb);
   mrb_bool key_p;
 
-  mrb_get_args(mrb, "o", &key);
   key_p = mrb_hash_key_p(mrb, hash, key);
   return mrb_bool_value(key_p);
 }
@@ -1331,10 +1325,9 @@ hash_has_value_i(mrb_state *mrb, mrb_value key, mrb_value val, void *p)
 static mrb_value
 mrb_hash_has_value(mrb_state *mrb, mrb_value hash)
 {
-  mrb_value val;
+  mrb_value val = mrb_get_arg1(mrb);
   struct has_v_arg arg;
   
-  mrb_get_args(mrb, "o", &val);
   arg.found = FALSE;
   arg.val = val;
   ht_foreach(mrb, RHASH_TBL(hash), hash_has_value_i, &arg);
diff --git a/src/kernel.c b/src/kernel.c
index ae9617686..8a78de67d 100644
--- a/src/kernel.c
+++ b/src/kernel.c
@@ -71,9 +71,8 @@ mrb_obj_inspect(mrb_state *mrb, mrb_value obj)
 static mrb_value
 mrb_equal_m(mrb_state *mrb, mrb_value self)
 {
-  mrb_value arg;
+  mrb_value arg = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &arg);
   return mrb_bool_value(mrb_equal(mrb, self, arg));
 }
 
@@ -471,9 +470,8 @@ mrb_obj_hash(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_obj_init_copy(mrb_state *mrb, mrb_value self)
 {
-  mrb_value orig;
+  mrb_value orig = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &orig);
   if (mrb_obj_equal(mrb, self, orig)) return self;
   if ((mrb_type(self) != mrb_type(orig)) || (mrb_obj_class(mrb, self) != mrb_obj_class(mrb, orig))) {
       mrb_raise(mrb, E_TYPE_ERROR, "initialize_copy should take same class object");
@@ -744,12 +742,11 @@ obj_respond_to(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_obj_ceqq(mrb_state *mrb, mrb_value self)
 {
-  mrb_value v;
+  mrb_value v = mrb_get_arg1(mrb);
   mrb_int i, len;
   mrb_sym eqq = mrb_intern_lit(mrb, "===");
   mrb_value ary = mrb_ary_splat(mrb, self);
 
-  mrb_get_args(mrb, "o", &v);
   len = RARRAY_LEN(ary);
   for (i=0; i<len; i++) {
     mrb_value c = mrb_funcall_argv(mrb, mrb_ary_entry(ary, i), eqq, 1, &v);
diff --git a/src/numeric.c b/src/numeric.c
index 07a2d20a8..3977a00c1 100644
--- a/src/numeric.c
+++ b/src/numeric.c
@@ -67,12 +67,11 @@ mrb_int_value(mrb_state *mrb, mrb_float f)
 static mrb_value
 integral_pow(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 #ifndef MRB_WITHOUT_FLOAT
   mrb_float d;
 #endif
 
-  mrb_get_args(mrb, "o", &y);
   if (mrb_fixnum_p(x) && mrb_fixnum_p(y)) {
     /* try ipow() */
     mrb_int base = mrb_fixnum(x);
@@ -116,9 +115,8 @@ static mrb_value
 integral_idiv(mrb_state *mrb, mrb_value x)
 {
 #ifdef MRB_WITHOUT_FLOAT
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   if (!mrb_fixnum_p(y)) {
     mrb_raise(mrb, E_TYPE_ERROR, "non fixnum value");
   }
@@ -154,9 +152,8 @@ static mrb_value
 integral_div(mrb_state *mrb, mrb_value x)
 {
 #ifdef MRB_WITHOUT_FLOAT
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   if (!mrb_fixnum_p(y)) {
     mrb_raise(mrb, E_TYPE_ERROR, "non fixnum value");
   }
@@ -271,9 +268,8 @@ flo_to_s(mrb_state *mrb, mrb_value flt)
 static mrb_value
 flo_minus(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   return mrb_float_value(mrb, mrb_float(x) - mrb_to_flo(mrb, y));
 }
 
@@ -289,9 +285,8 @@ flo_minus(mrb_state *mrb, mrb_value x)
 static mrb_value
 flo_mul(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   return mrb_float_value(mrb, mrb_float(x) * mrb_to_flo(mrb, y));
 }
 
@@ -351,11 +346,9 @@ flodivmod(mrb_state *mrb, double x, double y, mrb_float *divp, mrb_float *modp)
 static mrb_value
 flo_mod(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
   mrb_float mod;
 
-  mrb_get_args(mrb, "o", &y);
-
   flodivmod(mrb, mrb_float(x), mrb_to_flo(mrb, y), 0, &mod);
   return mrb_float_value(mrb, mod);
 }
@@ -376,9 +369,8 @@ flo_mod(mrb_state *mrb, mrb_value x)
 static mrb_value
 fix_eql(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   if (!mrb_fixnum_p(y)) return mrb_false_value();
   return mrb_bool_value(mrb_fixnum(x) == mrb_fixnum(y));
 }
@@ -387,9 +379,8 @@ fix_eql(mrb_state *mrb, mrb_value x)
 static mrb_value
 flo_eql(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   if (!mrb_float_p(y)) return mrb_false_value();
   return mrb_bool_value(mrb_float(x) == mrb_float(y));
 }
@@ -410,8 +401,7 @@ flo_eql(mrb_state *mrb, mrb_value x)
 static mrb_value
 flo_eq(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
-  mrb_get_args(mrb, "o", &y);
+  mrb_value y = mrb_get_arg1(mrb);
 
   switch (mrb_type(y)) {
   case MRB_TT_FIXNUM:
@@ -460,9 +450,8 @@ flo_rev(mrb_state *mrb, mrb_value x)
 static mrb_value
 flo_and(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
   int64_t v1, v2;
-  mrb_get_args(mrb, "o", &y);
 
   v1 = (int64_t)mrb_float(x);
   v2 = value_int64(mrb, y);
@@ -472,9 +461,8 @@ flo_and(mrb_state *mrb, mrb_value x)
 static mrb_value
 flo_or(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
   int64_t v1, v2;
-  mrb_get_args(mrb, "o", &y);
 
   v1 = (int64_t)mrb_float(x);
   v2 = value_int64(mrb, y);
@@ -484,9 +472,8 @@ flo_or(mrb_state *mrb, mrb_value x)
 static mrb_value
 flo_xor(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
   int64_t v1, v2;
-  mrb_get_args(mrb, "o", &y);
 
   v1 = (int64_t)mrb_float(x);
   v2 = value_int64(mrb, y);
@@ -847,9 +834,8 @@ mrb_num_mul(mrb_state *mrb, mrb_value x, mrb_value y)
 static mrb_value
 fix_mul(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   return fixnum_mul(mrb, x, y);
 }
 
@@ -894,10 +880,9 @@ fixdivmod(mrb_state *mrb, mrb_int x, mrb_int y, mrb_int *divp, mrb_int *modp)
 static mrb_value
 fix_mod(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
   mrb_int a, b;
 
-  mrb_get_args(mrb, "o", &y);
   a = mrb_fixnum(x);
    if (mrb_fixnum_p(y) && a != MRB_INT_MIN && (b=mrb_fixnum(y)) != MRB_INT_MIN) {
     mrb_int mod;
@@ -936,9 +921,7 @@ fix_mod(mrb_state *mrb, mrb_value x)
 static mrb_value
 fix_divmod(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
-
-  mrb_get_args(mrb, "o", &y);
+  mrb_value y = mrb_get_arg1(mrb);
 
   if (mrb_fixnum_p(y)) {
     mrb_int div, mod;
@@ -975,12 +958,10 @@ fix_divmod(mrb_state *mrb, mrb_value x)
 static mrb_value
 flo_divmod(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
   mrb_float div, mod;
   mrb_value a, b;
 
-  mrb_get_args(mrb, "o", &y);
-
   flodivmod(mrb, mrb_float(x), mrb_to_flo(mrb, y), &div, &mod);
   a = mrb_int_value(mrb, div);
   b = mrb_float_value(mrb, mod);
@@ -1003,9 +984,8 @@ flo_divmod(mrb_state *mrb, mrb_value x)
 static mrb_value
 fix_equal(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   switch (mrb_type(y)) {
   case MRB_TT_FIXNUM:
     return mrb_bool_value(mrb_fixnum(x) == mrb_fixnum(y));
@@ -1062,9 +1042,8 @@ static mrb_value flo_xor(mrb_state *mrb, mrb_value x);
 static mrb_value
 fix_and(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   bit_op(x, y, and, &);
 }
 
@@ -1079,9 +1058,8 @@ fix_and(mrb_state *mrb, mrb_value x)
 static mrb_value
 fix_or(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   bit_op(x, y, or, |);
 }
 
@@ -1096,9 +1074,8 @@ fix_or(mrb_state *mrb, mrb_value x)
 static mrb_value
 fix_xor(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   bit_op(x, y, or, ^);
 }
 
@@ -1320,9 +1297,8 @@ mrb_num_plus(mrb_state *mrb, mrb_value x, mrb_value y)
 static mrb_value
 fix_plus(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &other);
   return fixnum_plus(mrb, self, other);
 }
 
@@ -1378,9 +1354,8 @@ mrb_num_minus(mrb_state *mrb, mrb_value x, mrb_value y)
 static mrb_value
 fix_minus(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &other);
   return fixnum_minus(mrb, self, other);
 }
 
@@ -1497,10 +1472,9 @@ cmpnum(mrb_state *mrb, mrb_value v1, mrb_value v2)
 static mrb_value
 integral_cmp(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
   mrb_int n;
 
-  mrb_get_args(mrb, "o", &other);
   n = cmpnum(mrb, self, other);
   if (n == -2) return mrb_nil_value();
   return mrb_fixnum_value(n);
@@ -1515,10 +1489,9 @@ cmperr(mrb_state *mrb, mrb_value v1, mrb_value v2)
 static mrb_value
 integral_lt(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
   mrb_int n;
 
-  mrb_get_args(mrb, "o", &other);
   n = cmpnum(mrb, self, other);
   if (n == -2) cmperr(mrb, self, other);
   if (n < 0) return mrb_true_value();
@@ -1528,10 +1501,9 @@ integral_lt(mrb_state *mrb, mrb_value self)
 static mrb_value
 integral_le(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
   mrb_int n;
 
-  mrb_get_args(mrb, "o", &other);
   n = cmpnum(mrb, self, other);
   if (n == -2) cmperr(mrb, self, other);
   if (n <= 0) return mrb_true_value();
@@ -1541,10 +1513,9 @@ integral_le(mrb_state *mrb, mrb_value self)
 static mrb_value
 integral_gt(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
   mrb_int n;
 
-  mrb_get_args(mrb, "o", &other);
   n = cmpnum(mrb, self, other);
   if (n == -2) cmperr(mrb, self, other);
   if (n > 0) return mrb_true_value();
@@ -1554,10 +1525,9 @@ integral_gt(mrb_state *mrb, mrb_value self)
 static mrb_value
 integral_ge(mrb_state *mrb, mrb_value self)
 {
-  mrb_value other;
+  mrb_value other = mrb_get_arg1(mrb);
   mrb_int n;
 
-  mrb_get_args(mrb, "o", &other);
   n = cmpnum(mrb, self, other);
   if (n == -2) cmperr(mrb, self, other);
   if (n >= 0) return mrb_true_value();
@@ -1609,9 +1579,8 @@ num_infinite_p(mrb_state *mrb, mrb_value self)
 static mrb_value
 flo_plus(mrb_state *mrb, mrb_value x)
 {
-  mrb_value y;
+  mrb_value y = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &y);
   return mrb_float_value(mrb, mrb_float(x) + mrb_to_flo(mrb, y));
 }
 #endif
diff --git a/src/proc.c b/src/proc.c
index a7d9ee16b..df80682a2 100644
--- a/src/proc.c
+++ b/src/proc.c
@@ -211,9 +211,8 @@ mrb_proc_s_new(mrb_state *mrb, mrb_value proc_class)
 static mrb_value
 mrb_proc_init_copy(mrb_state *mrb, mrb_value self)
 {
-  mrb_value proc;
+  mrb_value proc = mrb_get_arg1(mrb);
 
-  mrb_get_args(mrb, "o", &proc);
   if (!mrb_proc_p(proc)) {
     mrb_raise(mrb, E_ARGUMENT_ERROR, "not a proc");
   }
diff --git a/src/range.c b/src/range.c
index 6df5d13a3..0b4e6dbca 100644
--- a/src/range.c
+++ b/src/range.c
@@ -182,11 +182,9 @@ range_eq(mrb_state *mrb, mrb_value range)
 {
   struct RRange *rr;
   struct RRange *ro;
-  mrb_value obj;
+  mrb_value obj = mrb_get_arg1(mrb);
   mrb_bool v1, v2;
 
-  mrb_get_args(mrb, "o", &obj);
-
   if (mrb_obj_equal(mrb, range, obj)) return mrb_true_value();
   if (!mrb_obj_is_instance_of(mrb, obj, mrb_obj_class(mrb, range))) { /* same class? */
     return mrb_false_value();
@@ -211,13 +209,11 @@ range_eq(mrb_state *mrb, mrb_value range)
 static mrb_value
 range_include(mrb_state *mrb, mrb_value range)
 {
-  mrb_value val;
+  mrb_value val = mrb_get_arg1(mrb);
   struct RRange *r = mrb_range_ptr(mrb, range);
   mrb_value beg, end;
   mrb_bool include_p;
 
-  mrb_get_args(mrb, "o", &val);
-
   beg = RANGE_BEG(r);
   end = RANGE_END(r);
   include_p = r_le(mrb, beg, val) &&                 /* beg <= val */
@@ -289,11 +285,9 @@ range_inspect(mrb_state *mrb, mrb_value range)
 static mrb_value
 range_eql(mrb_state *mrb, mrb_value range)
 {
-  mrb_value obj;
+  mrb_value obj = mrb_get_arg1(mrb);
   struct RRange *r, *o;
 
-  mrb_get_args(mrb, "o", &obj);
-
   if (mrb_obj_equal(mrb, range, obj)) return mrb_true_value();
   if (!mrb_obj_is_kind_of(mrb, obj, mrb->range_class)) return mrb_false_value();
   if (!mrb_range_p(obj)) return mrb_false_value();
@@ -312,11 +306,9 @@ range_eql(mrb_state *mrb, mrb_value range)
 static mrb_value
 range_initialize_copy(mrb_state *mrb, mrb_value copy)
 {
-  mrb_value src;
+  mrb_value src = mrb_get_arg1(mrb);
   struct RRange *r;
 
-  mrb_get_args(mrb, "o", &src);
-
   if (mrb_obj_equal(mrb, copy, src)) return copy;
   if (!mrb_obj_is_instance_of(mrb, src, mrb_obj_class(mrb, copy))) {
     mrb_raise(mrb, E_TYPE_ERROR, "wrong argument class");
diff --git a/src/string.c b/src/string.c
index 44e3c9069..e65747318 100644
--- a/src/string.c
+++ b/src/string.c
@@ -1061,10 +1061,9 @@ mrb_str_cmp(mrb_state *mrb, mrb_value str1, mrb_value str2)
 static mrb_value
 mrb_str_cmp_m(mrb_state *mrb, mrb_value str1)
 {
-  mrb_value str2;
+  mrb_value str2 = mrb_get_arg1(mrb);
   mrb_int result;
 
-  mrb_get_args(mrb, "o", &str2);
   if (!mrb_string_p(str2)) {
     return mrb_nil_value();
   }
@@ -1106,9 +1105,7 @@ mrb_str_equal(mrb_state *mrb, mrb_value str1, mrb_value str2)
 static mrb_value
 mrb_str_equal_m(mrb_state *mrb, mrb_value str1)
 {
-  mrb_value str2;
-
-  mrb_get_args(mrb, "o", &str2);
+  mrb_value str2 = mrb_get_arg1(mrb);
 
   return mrb_bool_value(mrb_str_equal(mrb, str1, str2));
 }
@@ -1791,10 +1788,9 @@ mrb_str_empty_p(mrb_state *mrb, mrb_value self)
 static mrb_value
 mrb_str_eql(mrb_state *mrb, mrb_value self)
 {
-  mrb_value str2;
+  mrb_value str2 = mrb_get_arg1(mrb);
   mrb_bool eql_p;
 
-  mrb_get_args(mrb, "o", &str2);
   eql_p = (mrb_string_p(str2)) && str_eql(mrb, self, str2);
 
   return mrb_bool_value(eql_p);
diff --git a/src/symbol.c b/src/symbol.c
index f55e09b7b..992848797 100644
--- a/src/symbol.c
+++ b/src/symbol.c
@@ -564,10 +564,9 @@ mrb_sym_dump(mrb_state *mrb, mrb_sym sym)
 static mrb_value
 sym_cmp(mrb_state *mrb, mrb_value s1)
 {
-  mrb_value s2;
+  mrb_value s2 = mrb_get_arg1(mrb);
   mrb_sym sym1, sym2;
 
-  mrb_get_args(mrb, "o", &s2);
   if (!mrb_symbol_p(s2)) return mrb_nil_value();
   sym1 = mrb_symbol(s1);
   sym2 = mrb_symbol(s2);