Remove mutex and simplify dimension handling

Lookups are now done via a slice where possible.

unittype.go

@@ -3,7 +3,6 @@ package unit
 import (
 	"sort"
 	"strconv"
-	"sync"
 )
 
 // Uniter is an interface representing a type that can be converted
@@ -37,11 +36,10 @@ const (
 	TimeDim
 	// Other common SI Dimensions
 	AngleDim // e.g. radians
-	lastPackageDimension // Used in create dimension
 )
 
-var lastCreatedDimension Dimension = lastPackageDimension
-var dimensionToSymbol map[Dimension]string = map[Dimension]string{
+var (
+	symbols = []string{
 		CurrentDim:           "A",
 		LengthDim:            "m",
 		LuminousIntensityDim: "cd",
@@ -49,8 +47,10 @@ var dimensionToSymbol map[Dimension]string = map[Dimension]string{
 		TemperatureDim:       "K",
 		TimeDim:              "s",
 		AngleDim:             "rad",
-}
-var symbolToDimension map[string]Dimension = map[string]Dimension{
+	}
+
+	// for guaranteeing there aren't two identical symbols
+	dimensions = map[string]Dimension{
 		"A":   CurrentDim,
 		"m":   LengthDim,
 		"cd":  LuminousIntensityDim,
@@ -113,7 +113,8 @@ var symbolToDimension map[string]Dimension = map[string]Dimension{
 		"R":   reserved,
 		"rd":  reserved,
 		"rem": reserved,
-} // for guaranteeing there aren't two identical symbols
+	}
+)
 
 // TODO: Should we actually reserve "common" SI unit symbols ("N", "J", etc.) so there isn't confusion
 // TODO: If we have a fancier ParseUnit, maybe the 'reserved' symbols should be a different map
@@ -124,8 +125,6 @@ var symbolToDimension map[string]Dimension = map[string]Dimension{
 // dimension is zero. Dimensions is used in conjuction with NewUnit
 type Dimensions map[Dimension]int
 
-var newUnitMutex *sync.Mutex = &sync.Mutex{} // so there is no race condition for dimension
-
 // NewDimension returns a new dimension variable which will have a
 // unique representation across packages to prevent accidental overlap.
 // The input string represents a symbol name which will be used for printing
@@ -138,18 +137,16 @@ var newUnitMutex *sync.Mutex = &sync.Mutex{} // so there is no race condition fo
 // if the symbol matching an existing symbol
 // NewDimension should only be called for unit types that are actually orthogonal
 // to the base dimensions defined in this package. Please see the package-level
-// documentation for further explanation
+// documentation for further explanation. Calls to NewDimension are not thread safe.
 func NewDimension(symbol string) Dimension {
-	newUnitMutex.Lock()
-	defer newUnitMutex.Unlock()
-	lastCreatedDimension++
-	_, ok := symbolToDimension[symbol]
+	_, ok := dimensions[symbol]
 	if ok {
 		panic("unit: dimension string " + symbol + " already used")
 	}
-	dimensionToSymbol[lastCreatedDimension] = symbol
-	symbolToDimension[symbol] = lastCreatedDimension
-	return lastCreatedDimension
+	symbols = append(symbols, symbol)
+	d := Dimension(len(symbols))
+	dimensions[symbol] = d
+	return d
 }
 
 // Unit is a type a value with generic SI units. Most useful for
@@ -272,7 +269,7 @@ func (u *Unit) String() string {
 	data := make(unitPrinters, 0, 10)
 	for dimension, power := range u.dimensions {
 		if power != 0 {
-			data = append(data, symbolString{dimensionToSymbol[dimension], power})
+			data = append(data, symbolString{symbols[dimension], power})
 		}
 	}
 	sort.Sort(data)