move struct spec logic into tags file

encode.go

@@ -7,7 +7,6 @@ import (
 	"io"
 	"reflect"
 	"strconv"
-	"sync"
 )
 
 // Marshal returns the fixed-width encoding of v.
@@ -166,41 +165,6 @@ func structEncoder(v reflect.Value) ([]byte, error) {
 	return dst, nil
 }
 
-type structSpec struct {
-	ll         int
-	fieldSpecs []fieldSpec
-}
-
-type fieldSpec struct {
-	startPos, endPos int
-	ok               bool
-}
-
-func buildStructSpec(t reflect.Type) structSpec {
-	ss := structSpec{
-		fieldSpecs: make([]fieldSpec, t.NumField()),
-	}
-	for i := 0; i < t.NumField(); i++ {
-		f := t.Field(i)
-		ss.fieldSpecs[i].startPos, ss.fieldSpecs[i].endPos, ss.fieldSpecs[i].ok = parseTag(f.Tag.Get("fixed"))
-		if ss.fieldSpecs[i].endPos > ss.ll {
-			ss.ll = ss.fieldSpecs[i].endPos
-		}
-	}
-	return ss
-}
-
-var fieldSpecCache sync.Map // map[reflect.Type]structSpec
-
-// cachedStructSpec is like buildStructSpec but cached to prevent duplicate work.
-func cachedStructSpec(t reflect.Type) structSpec {
-	if f, ok := fieldSpecCache.Load(t); ok {
-		return f.(structSpec)
-	}
-	f, _ := fieldSpecCache.LoadOrStore(t, buildStructSpec(t))
-	return f.(structSpec)
-}
-
 func textMarshalerEncoder(v reflect.Value) ([]byte, error) {
 	return v.Interface().(encoding.TextMarshaler).MarshalText()
 }

tags.go

@@ -1,8 +1,10 @@
 package fixedwidth
 
 import (
+	"reflect"
 	"strconv"
 	"strings"
+	"sync"
 )
 
 // parseTag splits a struct fields fixed tag into its start and end positions.
@@ -26,3 +28,39 @@ func parseTag(tag string) (startPos, endPos int, ok bool) {
 
 	return startPos, endPos, true
 }
+
+type structSpec struct {
+	// ll is the line length for the struct
+	ll         int
+	fieldSpecs []fieldSpec
+}
+
+type fieldSpec struct {
+	startPos, endPos int
+	ok               bool
+}
+
+func buildStructSpec(t reflect.Type) structSpec {
+	ss := structSpec{
+		fieldSpecs: make([]fieldSpec, t.NumField()),
+	}
+	for i := 0; i < t.NumField(); i++ {
+		f := t.Field(i)
+		ss.fieldSpecs[i].startPos, ss.fieldSpecs[i].endPos, ss.fieldSpecs[i].ok = parseTag(f.Tag.Get("fixed"))
+		if ss.fieldSpecs[i].endPos > ss.ll {
+			ss.ll = ss.fieldSpecs[i].endPos
+		}
+	}
+	return ss
+}
+
+var fieldSpecCache sync.Map // map[reflect.Type]structSpec
+
+// cachedStructSpec is like buildStructSpec but cached to prevent duplicate work.
+func cachedStructSpec(t reflect.Type) structSpec {
+	if f, ok := fieldSpecCache.Load(t); ok {
+		return f.(structSpec)
+	}
+	f, _ := fieldSpecCache.LoadOrStore(t, buildStructSpec(t))
+	return f.(structSpec)
+}