fixedpoint: add sort interface support on fixedpoint

pkg/fixedpoint/slice.go

@@ -5,3 +5,20 @@ type Slice []Value
 func (s Slice) Reduce(init Value, reducer Reducer) Value {
 	return Reduce(s, init, reducer)
 }
+
+// Defaults to ascending sort
+func (s Slice) Len() int           { return len(s) }
+func (s Slice) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s Slice) Less(i, j int) bool { return s[i].Compare(s[j]) < 0 }
+
+type Ascending []Value
+
+func (s Ascending) Len() int           { return len(s) }
+func (s Ascending) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s Ascending) Less(i, j int) bool { return s[i].Compare(s[j]) < 0 }
+
+type Descending []Value
+
+func (s Descending) Len() int           { return len(s) }
+func (s Descending) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
+func (s Descending) Less(i, j int) bool { return s[i].Compare(s[j]) > 0 }

pkg/fixedpoint/slice_test.go

@@ -0,0 +1,35 @@
+package fixedpoint
+
+import (
+	"sort"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestSortInterface(t *testing.T) {
+	slice := Slice{
+		NewFromInt(7),
+		NewFromInt(3),
+		NewFromInt(1),
+		NewFromInt(2),
+		NewFromInt(5),
+	}
+	sort.Sort(slice)
+	assert.Equal(t, "1", slice[0].String())
+	assert.Equal(t, "2", slice[1].String())
+	assert.Equal(t, "3", slice[2].String())
+	assert.Equal(t, "5", slice[3].String())
+
+	sort.Sort(Descending(slice))
+	assert.Equal(t, "7", slice[0].String())
+	assert.Equal(t, "5", slice[1].String())
+	assert.Equal(t, "3", slice[2].String())
+	assert.Equal(t, "2", slice[3].String())
+
+	sort.Sort(Ascending(slice))
+	assert.Equal(t, "1", slice[0].String())
+	assert.Equal(t, "2", slice[1].String())
+	assert.Equal(t, "3", slice[2].String())
+	assert.Equal(t, "5", slice[3].String())
+}