Update range to have exclusive and inclusive range.

lib/std/collections/range.c3

@@ -13,7 +13,7 @@ struct Range
 fn usz Range.len(Range* range) @operator(len)
 {
 	if (range.end < range.start) return 0;
-	return (usz)(range.end - range.start);
+	return (usz)(range.end - range.start + (Type)1);
 }
 
 /**
@@ -24,3 +24,22 @@ fn Type Range.get(Range* range, usz index) @operator([])
     return range.start + (Type)index;
 }
 
+struct ExclusiveRange
+{
+	Type start;
+	Type end;
+}
+
+fn usz ExclusiveRange.len(ExclusiveRange* range) @operator(len)
+{
+	if (range.end < range.start) return 0;
+	return (usz)(range.end - range.start);
+}
+
+/**
+ * @require index < range.len() : "Can't index into an empty range"
+ **/
+fn Type ExclusiveRange.get(ExclusiveRange* range, usz index) @operator([])
+{
+    return range.start + (Type)index;
+}

test/unit/stdlib/collections/range.c3

@@ -2,9 +2,11 @@ module range_test @test;
 import std::collections::range;
 
 def IntRange = Range<int>;
-fn void! test_range()
+def IntExRange = ExclusiveRange<int>;
+
+fn void! test_exrange()
 {
-	IntRange range = { -4, 2 };
+	IntExRange range = { -4, 2 };
 	int sum = 0;
 	foreach (int z : range)
 	{
@@ -12,4 +14,16 @@ fn void! test_range()
 		sum += z * z;
 	}
 	assert(sum == 31);
+}
+
+fn void! test_range()
+{
+	IntRange range = { -4, 2 };
+	int sum = 0;
+	foreach (int z : range)
+	{
+		assert(z >= -4 && z < 3);
+		sum += z * z;
+	}
+	assert(sum == 35);
 }