diff --git a/lib/std/collections/list.c3 b/lib/std/collections/list.c3
index 63514dfa7..4610a95e1 100644
--- a/lib/std/collections/list.c3
+++ b/lib/std/collections/list.c3
@@ -6,6 +6,7 @@ import std::io;
 import std::math;
 
 def ElementPredicate = fn bool(Type *type);
+def ElementTest = fn bool(Type *type, any context);
 const ELEMENT_IS_EQUATABLE = types::is_equatable_type(Type);
 const ELEMENT_IS_POINTER = Type.kindof == POINTER;
 
@@ -251,6 +252,15 @@ fn usz List.remove_if(&self, ElementPredicate filter)
 	return self._remove_if(filter, false);
 }
 
+/**
+ * @param selection "The function to determine if it should be kept or not"
+ * @return "the number of deleted elements"
+ **/
+fn usz List.retain_if(&self, ElementPredicate selection)
+{
+	return self._remove_if(selection, true);
+}
+
 macro usz List._remove_if(&self, ElementPredicate filter, bool $invert) @local
 {
 	usz size = self.size;
@@ -264,8 +274,7 @@ macro usz List._remove_if(&self, ElementPredicate filter, bool $invert) @local
 		$endif
 		// Remove the items from this index up to the one not to be deleted.
 		usz n = self.size - k;
-		// Do explicit copy - copying between the same slice is not well defined.
-		for (usz j = 0; j < n; j++) self.entries[i + j] = self.entries[k + j];
+		self.entries[i:n] = self.entries[k:n];
 		self.size -= k - i;
 		// Find last index of item not to be deleted.
 		$if $invert:
@@ -277,13 +286,39 @@ macro usz List._remove_if(&self, ElementPredicate filter, bool $invert) @local
 	return size - self.size;
 }
 
-/**
- * @param selection "The function to determine if it should be kept or not"
- * @return "the number of deleted elements"
- **/
-fn usz List.retain_if(&self, ElementPredicate selection)
+fn usz List.remove_using_test(&self, ElementTest filter, any context)
 {
-	return self._remove_if(selection, true);
+	return self._remove_using_test(filter, false, context);
+}
+
+fn usz List.retain_using_test(&self, ElementTest filter, any context)
+{
+	return self._remove_using_test(filter, true, context);
+}
+
+macro usz List._remove_using_test(&self, ElementTest filter, bool $invert, ctx) @local
+{
+	usz size = self.size;
+	for (usz i = size, usz k = size; k > 0; k = i)
+	{
+		// Find last index of item to be deleted.
+		$if $invert:
+			while (i > 0 && !filter(&self.entries[i - 1], ctx)) i--;
+		$else
+			while (i > 0 && filter(&self.entries[i - 1], ctx)) i--;
+		$endif
+		// Remove the items from this index up to the one not to be deleted.
+		usz n = self.size - k;
+		self.entries[i:n] = self.entries[k:n];
+		self.size -= k - i;
+		// Find last index of item not to be deleted.
+		$if $invert:
+			while (i > 0 && filter(&self.entries[i - 1], ctx)) i--;
+		$else
+			while (i > 0 && !filter(&self.entries[i - 1], ctx)) i--;
+		$endif
+	}
+	return size - self.size;
 }
 
 /**
diff --git a/test/unit/stdlib/collections/list.c3 b/test/unit/stdlib/collections/list.c3
index 2531a6dc7..3b34ab57e 100644
--- a/test/unit/stdlib/collections/list.c3
+++ b/test/unit/stdlib/collections/list.c3
@@ -78,6 +78,23 @@ fn void! remove_if()
 	assert(test.array_view() == int[]{11, 10, 20});
 }
 
+fn void! remove_using_test()
+{
+	IntList test;
+	usz removed;
+
+	test.add_array({ 1, 11, 2, 10, 20 });
+	removed = test.remove_using_test(fn bool(i, ctx) => *i >= *(int*)ctx, &&10);
+	assert(removed == 3);
+	assert(test.array_view() == int[]{1, 2});
+
+	test.clear();
+	test.add_array({ 1, 11, 2, 10, 20 });
+	removed = test.remove_using_test(fn bool(i, ctx) => *i < *(int*)ctx, &&10);
+	assert(removed == 2);
+	assert(test.array_view() == int[]{11, 10, 20});
+}
+
 fn void! retain_if()
 {
 	IntList test;
@@ -95,6 +112,23 @@ fn void! retain_if()
 	assert(test.array_view() == int[]{11, 10, 20});
 }
 
+fn void! retain_using_test()
+{
+	IntList test;
+	usz removed;
+
+	test.add_array({ 1, 11, 2, 10, 20 });
+	removed = test.remove_using_test(fn bool(i, ctx) => *i >= *(int*)ctx, &&10);
+	assert(removed == 3);
+	assert(test.array_view() == int[]{1, 2});
+
+	test.clear();
+	test.add_array({ 1, 11, 2, 10, 20 });
+	removed = test.remove_using_test(fn bool(i, ctx) => *i < *(int*)ctx, &&10);
+	assert(removed == 2);
+	assert(test.array_view() == int[]{11, 10, 20});
+}
+
 module list_test;
 
 fn bool filter(int* i)