Integrate the processing of similar specifiers of `mrb_get_args()`

It is `o`, `C`, `S`, `A` and `H` specifiers that are integrated.
As a side effect, the `C!` Specifier can now be used.

include/mruby.h

@@ -892,7 +892,7 @@ MRB_API struct RClass* mrb_define_module_under_id(mrb_state *mrb, struct RClass
  * | char | Ruby type      | C types           | Notes                                              |
  * |:----:|----------------|-------------------|----------------------------------------------------|
  * | `o`  | {Object}       | {mrb_value}       | Could be used to retrieve any type of argument     |
- * | `C`  | {Class}/{Module} | {mrb_value}     |                                                    |
+ * | `C`  | {Class}/{Module} | {mrb_value}     | when `!` follows, the value may be `nil`           |
  * | `S`  | {String}       | {mrb_value}       | when `!` follows, the value may be `nil`           |
  * | `A`  | {Array}        | {mrb_value}       | when `!` follows, the value may be `nil`           |
  * | `H`  | {Hash}         | {mrb_value}       | when `!` follows, the value may be `nil`           |

src/class.c

@@ -877,7 +877,7 @@ void mrb_hash_check_kdict(mrb_state *mrb, mrb_value self);
     string  mruby type     C type                 note
     ----------------------------------------------------------------------------------------------
     o:      Object         [mrb_value]
-    C:      Class/Module   [mrb_value]
+    C:      Class/Module   [mrb_value]            when ! follows, the value may be nil
     S:      String         [mrb_value]            when ! follows, the value may be nil
     A:      Array          [mrb_value]            when ! follows, the value may be nil
     H:      Hash           [mrb_value]            when ! follows, the value may be nil
@@ -1015,22 +1015,23 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
 
     switch (c) {
     case 'o':
-      {
-        mrb_value *p;
-
-        p = va_arg(ap, mrb_value*);
-        if (pickarg) {
-          *p = *pickarg;
-        }
-      }
-      break;
     case 'C':
+    case 'S':
+    case 'A':
+    case 'H':
       {
         mrb_value *p;
 
         p = va_arg(ap, mrb_value*);
         if (pickarg) {
-          ensure_class_type(mrb, *pickarg);
+          if (!(altmode && mrb_nil_p(*pickarg))) {
+            switch (c) {
+            case 'C': ensure_class_type(mrb, *pickarg); break;
+            case 'S': mrb_ensure_string_type(mrb, *pickarg); break;
+            case 'A': mrb_ensure_array_type(mrb, *pickarg); break;
+            case 'H': mrb_ensure_hash_type(mrb, *pickarg); break;
+            }
+          }
           *p = *pickarg;
         }
       }
@@ -1046,45 +1047,6 @@ mrb_get_args(mrb_state *mrb, const char *format, ...)
         }
       }
       break;
-    case 'S':
-      {
-        mrb_value *p;
-
-        p = va_arg(ap, mrb_value*);
-        if (pickarg) {
-          if (!(altmode && mrb_nil_p(*pickarg))) {
-            mrb_ensure_string_type(mrb, *pickarg);
-          }
-          *p = *pickarg;
-        }
-      }
-      break;
-    case 'A':
-      {
-        mrb_value *p;
-
-        p = va_arg(ap, mrb_value*);
-        if (pickarg) {
-          if (!(altmode && mrb_nil_p(*pickarg))) {
-            mrb_ensure_array_type(mrb, *pickarg);
-          }
-          *p = *pickarg;
-        }
-      }
-      break;
-    case 'H':
-      {
-        mrb_value *p;
-
-        p = va_arg(ap, mrb_value*);
-        if (pickarg) {
-          if (!(altmode && mrb_nil_p(*pickarg))) {
-            mrb_ensure_hash_type(mrb, *pickarg);
-          }
-          *p = *pickarg;
-        }
-      }
-      break;
     case 's':
       {
         const char **ps = 0;