Use concrete value for quad.Quad

Comparison of -short benchmarks in cayley.

$ benchcmp pointer.bench concrete.bench
benchmark                                   old ns/op     new ns/op	delta
BenchmarkNamePredicate                      1673276       1655093	-1.09%
BenchmarkLargeSetsNoIntersection            318985907     261499984	-18.02%
BenchmarkNetAndSpeed                        104403743     41516981	-60.23%
BenchmarkKeanuAndNet                        17309258      16857513	-2.61%
BenchmarkKeanuAndSpeed                      20159161      19282833	-4.35%

Comparison of pathological cases are not so happy.

benchmark                                   old ns/op       new ns/op		delta
BenchmarkVeryLargeSetsSmallIntersection     55269775527     246084606672	+345.24%
BenchmarkHelplessContainsChecker            23436501319     24308906949		+3.72%

Profiling the worst case:

Pointer:
Total: 6121 samples
    1973  32.2%  32.2%     1973  32.2% runtime.findfunc
     773  12.6%  44.9%      773  12.6% readvarint
     510   8.3%  53.2%      511   8.3% step
     409   6.7%  59.9%      410   6.7% runtime.gentraceback
     390   6.4%  66.2%      391   6.4% pcvalue
     215   3.5%  69.8%      215   3.5% runtime.funcdata
     181   3.0%  72.7%      181   3.0% checkframecopy
     118   1.9%  74.6%      119   1.9% runtime.funcspdelta
      96   1.6%  76.2%       96   1.6% runtime.topofstack
      76   1.2%  77.5%       76   1.2% scanblock

Concrete:
Total: 25027 samples
    9437  37.7%  37.7%     9437  37.7% runtime.findfunc
    3853  15.4%  53.1%     3853  15.4% readvarint
    2366   9.5%  62.6%     2366   9.5% step
    2186   8.7%  71.3%     2186   8.7% runtime.gentraceback
    1816   7.3%  78.5%     1816   7.3% pcvalue
    1016   4.1%  82.6%     1016   4.1% runtime.funcdata
     859   3.4%  86.0%      859   3.4% checkframecopy
     506   2.0%  88.1%      506   2.0% runtime.funcspdelta
     410   1.6%  89.7%      410   1.6% runtime.topofstack
     303   1.2%  90.9%      303   1.2% runtime.newstack

quad/quad.go

@@ -104,7 +104,7 @@ func (d Direction) String() string {
 // instead of the pointer. This needs benchmarking to make the decision.
 
 // Per-field accessor for triples
-func (q *Quad) Get(d Direction) string {
+func (q Quad) Get(d Direction) string {
 	switch d {
 	case Subject:
 		return q.Subject
@@ -119,16 +119,16 @@ func (q *Quad) Get(d Direction) string {
 	}
 }
 
-func (q *Quad) Equals(o *Quad) bool {
-	return *q == *o
+func (q Quad) Equals(o Quad) bool {
+	return q == o
 }
 
 // Pretty-prints a triple.
-func (q *Quad) String() string {
+func (q Quad) String() string {
 	return fmt.Sprintf("%s -- %s -> %s", q.Subject, q.Predicate, q.Object)
 }
 
-func (q *Quad) IsValid() bool {
+func (q Quad) IsValid() bool {
 	return q.Subject != "" && q.Predicate != "" && q.Object != ""
 }
 
@@ -137,7 +137,7 @@ func (q *Quad) IsValid() bool {
 // from nquads to here to provide UnmarshalText(text []byte) error.
 
 // Prints a triple in N-Quad format.
-func (q *Quad) NTriple() string {
+func (q Quad) NTriple() string {
 	if q.Label == "" {
 		//TODO(barakmich): Proper escaping.
 		return fmt.Sprintf("%s %s %s .", q.Subject, q.Predicate, q.Object)
@@ -147,5 +147,5 @@ func (q *Quad) NTriple() string {
 }
 
 type Unmarshaler interface {
-	Unmarshal() (*Quad, error)
+	Unmarshal() (Quad, error)
 }