Add replace and updateSpans to SpanIndex.

spec/atom/span-index-spec.coffee

@@ -5,6 +5,16 @@ describe "SpanIndex", ->
   beforeEach ->
     index = new SpanIndex
 
+  describe ".updateSpans(start, end, spans)", ->
+    it "updates the spans of a range of entries indicated by the given index to the given value", ->
+      index.insert(0, [3, 2, 3, 1, 2], ['a', 'b', 'c', 'd', 'e'])
+      index.updateSpans(1, 3, 1)
+      expect(index.spanForIndex(1)).toBe 3
+      expect(index.spanForIndex(2)).toBe 4
+      expect(index.spanForIndex(3)).toBe 5
+      expect(index.spanForIndex(4)).toBe 6
+      expect(index.spanForIndex(5)).toBe 8
+
   describe ".sliceBySpan(start, end)", ->
     describe "when the index contains values that start and end evenly on the given start/end span indices", ->
       it "returns the spanning values with a start and end offset of 0", ->

src/atom/span-index.coffee

@@ -8,9 +8,16 @@ class SpanIndex
   insert: (index, spans, values) ->
     @entries[index..index] = @buildIndexEntries(spans, values)
 
+  replace: (index, span, value) ->
+    @splice(index, index, span, [value])
+
   splice: (start, end, spans, values) ->
     @entries[start..end] = @buildIndexEntries(spans, values)
 
+  updateSpans: (start, end, span) ->
+    for i in [start..end]
+      @entries[i].span = span
+
   at: (index) ->
     @entries[index].value