From 4b7f7b349e906e4760279273f1c03ad5fa802e25 Mon Sep 17 00:00:00 2001
From: Charlie Stanton <charlie@shtanton.xyz>
Date: Fri, 21 Apr 2023 14:25:08 +0100
Subject: Improves performance by being more explicit about memory allocation
 in walk.go

---
 walk/walk.go | 61 +++++++++++++++++++++++++++++++-----------------------------
 1 file changed, 32 insertions(+), 29 deletions(-)

(limited to 'walk/walk.go')

diff --git a/walk/walk.go b/walk/walk.go
index 48aff34..6d00ef2 100644
--- a/walk/walk.go
+++ b/walk/walk.go
@@ -65,7 +65,6 @@ func (value TerminalValue) String() string {
 			panic("Unknown TerminalValue")
 	}
 }
-func (value TerminalValue) atomness() {}
 
 type ValueNull struct {}
 func (value ValueNull) Atomise() []Atom {
@@ -74,7 +73,6 @@ func (value ValueNull) Atomise() []Atom {
 func (value ValueNull) String() string {
 	return "null"
 }
-func (value ValueNull) atomness() {}
 
 type ValueBool bool
 func (value ValueBool) Atomise() []Atom {
@@ -87,7 +85,6 @@ func (value ValueBool) String() string {
 		return "false"
 	}
 }
-func (value ValueBool) atomness() {}
 
 type ValueNumber float64
 func (value ValueNumber) Atomise() []Atom {
@@ -97,13 +94,16 @@ func (value ValueNumber) String() string {
 	v := float64(value)
 	return fmt.Sprintf("%f", v)
 }
-func (value ValueNumber) atomness() {}
 
 type StringTerminal struct {}
-func (value StringTerminal) atomness() {}
+func (value StringTerminal) String() string {
+	return "\""
+}
 
 type StringAtom rune
-func (value StringAtom) atomness() {}
+func (value StringAtom) String() string {
+	return string(value)
+}
 
 type ValueString string
 func (value ValueString) Atomise() (out []Atom) {
@@ -119,8 +119,7 @@ func (value ValueString) String() string {
 }
 
 type Atom interface {
-	// Something so the compiler will check that only certain types are being cast into Atoms
-	atomness()
+	String() string
 }
 
 type WalkValue interface {
@@ -421,10 +420,14 @@ func JsonOut(in chan WalkItem) {
 }
 
 func ConcatData(first []Atom, second []Atom) []Atom {
-	return append(append([]Atom(nil), first...), second...)
+	res := make([]Atom, 0, len(first) + len(second))
+	res = append(res, first...)
+	res = append(res, second...)
+	return res
 }
 
 func Atomise(in []WalkValue) (out []Atom) {
+	out = make([]Atom, 0, len(in) * 2)
 	for _, value := range in {
 		out = append(out, value.Atomise()...)
 	}
@@ -461,7 +464,24 @@ type CompoundResult struct {
 }
 
 func Compound(in []Atom) (out []WalkValue, error error) {
+	numValues := 0
 	i := 0
+	inString := false
+	for _, atom := range in {
+		switch atom.(type) {
+			case TerminalValue, ValueNull, ValueBool, ValueNumber:
+				if !inString {
+					numValues++
+				}
+			case StringTerminal:
+				if inString {
+					numValues++
+				}
+				inString = !inString
+		}
+	}
+	i = 0
+	out = make([]WalkValue, 0, numValues)
 	for {
 		if i >= len(in) {
 			break
@@ -469,17 +489,8 @@ func Compound(in []Atom) (out []WalkValue, error error) {
 		atom := in[i]
 		i++
 		switch v := atom.(type) {
-			case TerminalValue:
-				out = append(out, v)
-				continue
-			case ValueNull:
-				out = append(out, v)
-				continue
-			case ValueBool:
-				out = append(out, v)
-				continue
-			case ValueNumber:
-				out = append(out, v)
+			case TerminalValue, ValueNull, ValueBool, ValueNumber:
+				out = append(out, v.(WalkValue))
 				continue
 			case StringAtom:
 				return nil, CompoundRuneOutsideString
@@ -498,15 +509,7 @@ func Compound(in []Atom) (out []WalkValue, error error) {
 			switch v := atom.(type) {
 				case StringTerminal:
 					break loop
-				case StringAtom:
-					builder.WriteRune(rune(v))
-				case ValueNull:
-					builder.WriteString(v.String())
-				case ValueBool:
-					builder.WriteString(v.String())
-				case ValueNumber:
-					builder.WriteString(v.String())
-				case TerminalValue:
+				case StringAtom, ValueNull, ValueBool, ValueNumber, TerminalValue:
 					builder.WriteString(v.String())
 				default:
 					return nil, CompoundInvalidStringAtom
-- 
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