Benchmark what a bound draw costs

bench_test.go

@@ -57,6 +57,31 @@ func BenchmarkRepeat(b *testing.B) {
 	benchPath(b, dir, "many")
 }
 
+// BenchmarkBound measures a format that binds a head and reads two paths from it —
+// what a correlated pair costs against BenchmarkUnbound, the same output drawn from
+// two independent fields.
+func BenchmarkBound(b *testing.B) {
+	dir := tmpData(b, "addr", `{"format":"{place.postal-code} {place.locality}","place":[
+		{"format":"{locality}","locality":"Stockholm","postal-code":{"format":"#100 00"}},
+		{"format":"{locality}","locality":"Tranås","postal-code":{"format":"#5#7#3 00"}}]}`)
+	benchPath(b, dir, "addr")
+}
+
+func BenchmarkUnbound(b *testing.B) {
+	dir := tmpData(b, "addr", `{"format":"{postal-code} {locality}",
+		"postal-code":[{"format":"#100 00"},{"format":"#5#7#3 00"}],
+		"locality":["Stockholm","Tranås"]}`)
+	benchPath(b, dir, "addr")
+}
+
+// BenchmarkBoundDeep reads two paths through an intermediate level, the shape the
+// depth question is about.
+func BenchmarkBoundDeep(b *testing.B) {
+	dir := tmpData(b, "addr", `{"format":"{p.addr.city} {p.addr.zip}","p":[
+		{"format":"{addr}","addr":{"format":"{city}","city":["Stockholm","Tranås"],"zip":{"format":"#100 00"}}}]}`)
+	benchPath(b, dir, "addr")
+}
+
 // BenchmarkNew measures load+compile+validate of the whole shipped tree.
 func BenchmarkNew(b *testing.B) {
 	b.ReportAllocs()