String::release and String::reset methods

Rename reassociate to reset and create an inverse method release.
Method names are chosen to match std::unique_ptr methods.

sql/item_strfunc.cc

@@ -4583,8 +4583,7 @@ String *Item_func_dyncol_create::val_str(String *str)
       char *ptr;
       size_t length, alloc_length;
       dynstr_reassociate(&col, &ptr, &length, &alloc_length);
-      str_value.reassociate(ptr, (uint32) length, (uint32) alloc_length,
-                            &my_charset_bin);
+      str_value.reset(ptr, length, alloc_length, &my_charset_bin);
       res= &str_value;
       null_value= FALSE;
     }
@@ -4676,8 +4675,7 @@ String *Item_func_dyncol_json::val_str(String *str)
     char *ptr;
     size_t length, alloc_length;
     dynstr_reassociate(&json, &ptr, &length, &alloc_length);
-    str->reassociate(ptr, (uint32) length, (uint32) alloc_length,
-                     &my_charset_utf8_general_ci);
+    str->reset(ptr, length, alloc_length, &my_charset_utf8_general_ci);
     null_value= FALSE;
   }
   return str;
@@ -4725,8 +4723,7 @@ String *Item_func_dyncol_add::val_str(String *str)
     char *ptr;
     size_t length, alloc_length;
     dynstr_reassociate(&col, &ptr, &length, &alloc_length);
-    str->reassociate(ptr, (uint32) length, (uint32) alloc_length,
-                     &my_charset_bin);
+    str->reset(ptr, length, alloc_length, &my_charset_bin);
     null_value= FALSE;
   }
 

sql/sql_string.h

@@ -257,9 +257,9 @@ class String
   bool set(ulonglong num, CHARSET_INFO *cs) { return set_int((longlong)num, true, cs); }
   bool set_real(double num,uint decimals, CHARSET_INFO *cs);
 
-  /* Move handling of buffer from some other object to String */
-  void reassociate(char *ptr_arg, uint32 length_arg, uint32 alloced_length_arg,
-                   CHARSET_INFO *cs)
+  /* Take over handling of buffer from some other object */
+  void reset(char *ptr_arg, uint32 length_arg, uint32 alloced_length_arg,
+             CHARSET_INFO *cs)
   { 
     free();
     Ptr= ptr_arg;
@@ -269,6 +269,15 @@ class String
     alloced= ptr_arg != 0;
   }
 
+  /* Forget about the buffer, let some other object handle it */
+  char *release()
+  {
+    char *old= Ptr;
+    Ptr=0; str_length= Alloced_length= extra_alloc= 0;
+    alloced= thread_specific= 0;
+    return old;
+  }
+
   /*
     PMG 2004.11.12
     This is a method that works the same as perl's "chop". It simply