From: Lucas Bajolet <r4pass@hotmail.com>
Date: Fri, 6 May 2016 20:32:45 +0000 (-0400)
Subject: lib/core: Added new `append_substring` service to avoid creating ephemeral instances
X-Git-Url: http://nitlanguage.org

lib/core: Added new `append_substring` service to avoid creating ephemeral instances

Signed-off-by: Lucas Bajolet <r4pass@hotmail.com>
---

diff --git a/lib/core/text/abstract_text.nit b/lib/core/text/abstract_text.nit
index 6c2acd4..c9d1279 100644
--- a/lib/core/text/abstract_text.nit
+++ b/lib/core/text/abstract_text.nit
@@ -1514,6 +1514,42 @@ abstract class Buffer
 	# In Buffers, the internal sequence of character is mutable
 	# Thus, `chars` can be used to modify the buffer.
 	redef fun chars: Sequence[Char] is abstract
+
+	# Appends `length` chars from `s` starting at index `from`
+	#
+	# ~~~nit
+	#	var b = new Buffer
+	#	b.append_substring("abcde", 1, 2)
+	#	assert b == "bc"
+	#	b.append_substring("vwxyz", 2, 3)
+	#	assert b == "bcxyz"
+	#	b.append_substring("ABCDE", 4, 300)
+	#	assert b == "bcxyzE"
+	#	b.append_substring("VWXYZ", 400, 1)
+	#	assert b == "bcxyzE"
+	# ~~~
+	fun append_substring(s: Text, from, length: Int) do
+		if from < 0 then
+			length += from
+			from = 0
+		end
+		var ln = s.length
+		if (length + from) > ln then length = ln - from
+		if length <= 0 then return
+		append_substring_impl(s, from, length)
+	end
+
+	# Unsafe version of `append_substring` for performance
+	#
+	# NOTE: Use only if sure about `from` and `length`, no checks
+	# or bound recalculation is done
+	fun append_substring_impl(s: Text, from, length: Int) do
+		var pos = from
+		for i in [0 .. length[ do
+			self.add s[pos]
+			pos += 1
+		end
+	end
 end
 
 # View for chars on Buffer objects, extends Sequence
diff --git a/lib/core/text/flat.nit b/lib/core/text/flat.nit
index 45ad144..83cae37 100644
--- a/lib/core/text/flat.nit
+++ b/lib/core/text/flat.nit
@@ -411,7 +411,7 @@ abstract class FlatString
 
 		if from < 0 then
 			count += from
-			if count < 0 then return ""
+			if count <= 0 then return ""
 			from = 0
 		end
 
@@ -1054,6 +1054,21 @@ class FlatBuffer
 		return new FlatBuffer.with_infos(r_items, byte_length, byte_length, count)
 	end
 
+	redef fun append_substring_impl(s, from, length) do
+		if length <= 0 then return
+		if not s isa FlatText then
+			super
+			return
+		end
+		var bytest = s.char_to_byte_index(from)
+		var bytend = s.char_to_byte_index(from + length - 1)
+		var btln = bytend - bytest + 1
+		enlarge(btln + _bytelen)
+		s._items.copy_to(_items, btln, bytest, _bytelen)
+		_bytelen += btln
+		_length += length
+	end
+
 	redef fun reverse
 	do
 		written = false