support String#[]= with 3 args

1 files changed, 42 insertions, 7 deletions

diff --git a/mrblib/string.rb b/mrblib/string.rb
index 05b13cb43..5765cff9b 100644
--- a/mrblib/string.rb
+++ b/mrblib/string.rb
@@ -154,13 +154,48 @@ class String
   end
 
   ##
-  # Modify +self+ by replacing the content of +self+
-  # at the position +pos+ with +value+.
-  def []=(pos, value)
-    pos += self.length if pos < 0
-    b = self[0, pos]
-    a = self[pos + 1..-1]
-    self.replace([b, value, a].join(''))
+  # Modify +self+ by replacing the content of +self+.
+  # The portion of the string affected is determined using the same criteria as +String#[]+.
+  def []=(*args)
+    anum = args.size
+    if anum == 2
+      pos, value = args
+      if pos.kind_of? String
+        posnum = self.index(pos)
+        if posnum
+          b = self[0, posnum.to_i]
+          a = self[(posnum + pos.length)..-1]
+          self.replace([b, value, a].join(''))
+          return value
+        else
+          raise IndexError, "string not matched"
+        end
+      else
+        pos += self.length if pos < 0
+        if pos < 0 || pos > self.length
+          raise IndexError, "index #{args[0]} out of string"
+        end
+        b = self[0, pos.to_i]
+        a = self[pos + 1..-1]
+        self.replace([b, value, a].join(''))
+        return value
+      end
+    elsif anum == 3
+      pos, len, value = args
+      pos += self.length if pos < 0
+      if pos < 0 || pos > self.length
+        raise IndexError, "index #{args[0]} out of string"
+      end
+      if len < 0
+        raise IndexError, "negative length #{len}"
+      end
+      b = self[0, pos.to_i]
+      a = self[pos + len..-1]
+      self.replace([b, value, a].join(''))
+      return value
+    else
+      raise ArgumentError, "wrong number of arguments (#{anum} for 2..3)"
+    end
   end
 
   ##