Micro-optimizations

- Make structs smaller
- Introduce Result struct and use it to represent matched items instead of
  reusing Item struct for that purpose
- Avoid unnecessary memory allocation
- Avoid growing slice from the initial capacity
- Code cleanup

src/merger.go

@@ -3,13 +3,13 @@ package fzf
 import "fmt"
 
 // EmptyMerger is a Merger with no data
-var EmptyMerger = NewMerger([][]*Item{}, false, false)
+var EmptyMerger = NewMerger([][]*Result{}, false, false)
 
 // Merger holds a set of locally sorted lists of items and provides the view of
 // a single, globally-sorted list
 type Merger struct {
-	lists   [][]*Item
-	merged  []*Item
+	lists   [][]*Result
+	merged  []*Result
 	chunks  *[]*Chunk
 	cursors []int
 	sorted  bool
@@ -33,10 +33,10 @@ func PassMerger(chunks *[]*Chunk, tac bool) *Merger {
 }
 
 // NewMerger returns a new Merger
-func NewMerger(lists [][]*Item, sorted bool, tac bool) *Merger {
+func NewMerger(lists [][]*Result, sorted bool, tac bool) *Merger {
 	mg := Merger{
 		lists:   lists,
-		merged:  []*Item{},
+		merged:  []*Result{},
 		chunks:  nil,
 		cursors: make([]int, len(lists)),
 		sorted:  sorted,
@@ -55,14 +55,14 @@ func (mg *Merger) Length() int {
 	return mg.count
 }
 
-// Get returns the pointer to the Item object indexed by the given integer
-func (mg *Merger) Get(idx int) *Item {
+// Get returns the pointer to the Result object indexed by the given integer
+func (mg *Merger) Get(idx int) *Result {
 	if mg.chunks != nil {
 		if mg.tac {
 			idx = mg.count - idx - 1
 		}
 		chunk := (*mg.chunks)[idx/chunkSize]
-		return (*chunk)[idx%chunkSize]
+		return &Result{item: (*chunk)[idx%chunkSize]}
 	}
 
 	if mg.sorted {
@@ -86,9 +86,9 @@ func (mg *Merger) cacheable() bool {
 	return mg.count < mergerCacheMax
 }
 
-func (mg *Merger) mergedGet(idx int) *Item {
+func (mg *Merger) mergedGet(idx int) *Result {
 	for i := len(mg.merged); i <= idx; i++ {
-		minRank := buildEmptyRank(0)
+		minRank := minRank()
 		minIdx := -1
 		for listIdx, list := range mg.lists {
 			cursor := mg.cursors[listIdx]
@@ -97,7 +97,7 @@ func (mg *Merger) mergedGet(idx int) *Item {
 				continue
 			}
 			if cursor >= 0 {
-				rank := list[cursor].Rank(false)
+				rank := list[cursor].rank
 				if minIdx < 0 || compareRanks(rank, minRank, mg.tac) {
 					minRank = rank
 					minIdx = listIdx