Add String#prepend

mrbgems/mruby-string-ext/src/string.c

@@ -331,6 +331,44 @@ mrb_str_succ(mrb_state *mrb, mrb_value self)
   return str;
 }
 
+/*
+ *  call-seq:
+ *     str.prepend(other_str)  -> str
+ *
+ *  Prepend---Prepend the given string to <i>str</i>.
+ *
+ *     a = "world"
+ *     a.prepend("hello ") #=> "hello world"
+ *     a                   #=> "hello world"
+ */
+static mrb_value
+mrb_str_prepend(mrb_state *mrb, mrb_value self)
+{
+  struct RString *s1 = mrb_str_ptr(self), *s2, *temp_s;
+  mrb_int len;
+  mrb_value other, temp_str;
+
+  mrb_get_args(mrb, "S", &other);
+
+  mrb_str_modify(mrb, s1);
+  if (!mrb_string_p(other)) {
+    other = mrb_str_to_str(mrb, other);
+  }
+  s2 = mrb_str_ptr(other);
+  len = RSTR_LEN(s1) + RSTR_LEN(s2);
+  temp_str = mrb_str_new(mrb, "", RSTR_LEN(s1));
+  temp_s = mrb_str_ptr(temp_str);
+  memcpy(RSTR_PTR(temp_s), RSTR_PTR(s1), RSTR_LEN(s1));
+  if (RSTRING_CAPA(self) < len) {
+    mrb_str_resize(mrb, self, len);
+  }
+  memcpy(RSTR_PTR(s1), RSTR_PTR(s2), RSTR_LEN(s2));
+  memcpy(RSTR_PTR(s1) + RSTR_LEN(s2), RSTR_PTR(temp_s), RSTR_LEN(temp_s));
+  RSTR_SET_LEN(s1, len);
+  RSTR_PTR(s1)[len] = '\0';
+  return self;
+}
+
 void
 mrb_mruby_string_ext_gem_init(mrb_state* mrb)
 {
@@ -350,6 +388,7 @@ mrb_mruby_string_ext_gem_init(mrb_state* mrb)
   mrb_define_method(mrb, s, "lines",           mrb_str_lines,           MRB_ARGS_NONE());
   mrb_define_method(mrb, s, "succ",            mrb_str_succ,            MRB_ARGS_NONE());
   mrb_define_method(mrb, s, "succ!",           mrb_str_succ_bang,       MRB_ARGS_NONE());
+  mrb_define_method(mrb, s, "prepend",         mrb_str_prepend,         MRB_ARGS_REQ(1));
   mrb_alias_method(mrb, s, mrb_intern_lit(mrb, "next"), mrb_intern_lit(mrb, "succ"));
   mrb_alias_method(mrb, s, mrb_intern_lit(mrb, "next!"), mrb_intern_lit(mrb, "succ!"));
 }

mrbgems/mruby-string-ext/test/string.rb

@@ -380,3 +380,9 @@ assert('String#insert') do
   assert_raise(IndexError) { "abcd".insert(5, 'X') }
   assert_raise(IndexError) { "abcd".insert(-6, 'X') }
 end
+
+assert('String#prepend') do
+  a = "world"
+  assert_equal "hello world", a.prepend("hello ")
+  assert_equal "hello world", a
+end