add String#freeze to the core

include/mruby/string.h

@@ -59,6 +59,10 @@ struct RString {
 #define RSTR_SET_NOFREE_FLAG(s) ((s)->flags |= MRB_STR_NOFREE)
 #define RSTR_UNSET_NOFREE_FLAG(s) ((s)->flags &= ~MRB_STR_NOFREE)
 
+#define RSTR_FROZEN_P(s) ((s)->flags & MRB_STR_FROZEN)
+#define RSTR_SET_FROZEN_FLAG(s) ((s)->flags |= MRB_STR_FROZEN)
+#define RSTR_UNSET_FROZEN_FLAG(s) ((s)->flags &= ~MRB_STR_FROZEN)
+
 #define mrb_str_ptr(s)       ((struct RString*)(mrb_ptr(s)))
 #define RSTRING(s)           mrb_str_ptr(s)
 #define RSTRING_PTR(s)       RSTR_PTR(RSTRING(s))
@@ -70,9 +74,10 @@ mrb_int mrb_str_strlen(mrb_state*, struct RString*);
 
 #define MRB_STR_SHARED    1
 #define MRB_STR_NOFREE    2
-#define MRB_STR_EMBED     4
-#define MRB_STR_EMBED_LEN_MASK 0xf8
-#define MRB_STR_EMBED_LEN_SHIFT 3
+#define MRB_STR_FROZEN    4
+#define MRB_STR_EMBED     8
+#define MRB_STR_EMBED_LEN_MASK 0x1f0
+#define MRB_STR_EMBED_LEN_SHIFT 4
 
 void mrb_gc_free_str(mrb_state*, struct RString*);
 MRB_API void mrb_str_modify(mrb_state*, struct RString*);

src/string.c

@@ -75,9 +75,18 @@ str_decref(mrb_state *mrb, mrb_shared_string *shared)
   }
 }
 
+static void
+check_frozen(mrb_state *mrb, struct RString *s)
+{
+  if (RSTR_FROZEN_P(s)) {
+    mrb_raise(mrb, E_RUNTIME_ERROR, "can't modify frozen string");
+  }
+}
+
 MRB_API void
 mrb_str_modify(mrb_state *mrb, struct RString *s)
 {
+  check_frozen(mrb, s);
   if (RSTR_SHARED_P(s)) {
     mrb_shared_string *shared = s->as.heap.aux.shared;
 
@@ -119,6 +128,15 @@ mrb_str_modify(mrb_state *mrb, struct RString *s)
   }
 }
 
+static mrb_value
+mrb_str_freeze(mrb_state *mrb, mrb_value str)
+{
+  struct RString *s = mrb_str_ptr(str);
+
+  RSTR_SET_FROZEN_FLAG(s);
+  return str;
+}
+
 MRB_API mrb_value
 mrb_str_resize(mrb_state *mrb, mrb_value str, mrb_int len)
 {
@@ -1345,6 +1363,7 @@ str_replace(mrb_state *mrb, struct RString *s1, struct RString *s2)
 {
   long len;
 
+  check_frozen(mrb, s1);
   len = RSTR_LEN(s2);
   if (RSTR_SHARED_P(s1)) {
     str_decref(mrb, s1->as.heap.aux.shared);
@@ -2514,4 +2533,6 @@ mrb_init_string(mrb_state *mrb)
   mrb_define_method(mrb, s, "upcase!",         mrb_str_upcase_bang,     MRB_ARGS_NONE()); /* 15.2.10.5.43 */
   mrb_define_method(mrb, s, "inspect",         mrb_str_inspect,         MRB_ARGS_NONE()); /* 15.2.10.5.46(x) */
   mrb_define_method(mrb, s, "bytes",           mrb_str_bytes,           MRB_ARGS_NONE());
+
+  mrb_define_method(mrb, s, "freeze",          mrb_str_freeze,          MRB_ARGS_NONE());
 }