refactor(range): compute formatted value lazily

This speeds bench-subset and bench-satisfies by up to 9%.

The external interface of the Range class is kept as-is except that the .range property is not writable anymore.

classes/range.js

@@ -20,7 +20,7 @@ class Range {
       // just put it in the set and return
       this.raw = range.value
       this.set = [[range]]
-      this.format()
+      this.formatted = undefined
       return this
     }
 
@@ -65,23 +65,29 @@ class Range {
       }
     }
 
-    this.format()
+    this.formatted = undefined
   }
 
-  format () {
-    this.range = ''
-    for (let i = 0; i < this.set.length; i++) {
-      if (i > 0) {
-        this.range += '||'
-      }
-      const comps = this.set[i]
-      for (let k = 0; k < comps.length; k++) {
-        if (k > 0) {
-          this.range += ' '
+  get range () {
+    if (this.formatted === undefined) {
+      this.formatted = ''
+      for (let i = 0; i < this.set.length; i++) {
+        if (i > 0) {
+          this.formatted += '||'
+        }
+        const comps = this.set[i]
+        for (let k = 0; k < comps.length; k++) {
+          if (k > 0) {
+            this.formatted += ' '
+          }
+          this.formatted += comps[k].toString().trim()
         }
-        this.range += comps[k].toString().trim()
       }
     }
+    return this.formatted
+  }
+
+  format () {
     return this.range
   }
 

test/classes/range.js

@@ -82,6 +82,13 @@ test('tostrings', (t) => {
   t.end()
 })
 
+test('format', (t) => {
+  const r = new Range('>= v1.2.3')
+  t.equal(r.format(), '>=1.2.3')
+  t.equal(r.format(), '>=1.2.3')
+  t.end()
+})
+
 test('ranges intersect', (t) => {
   rangeIntersection.forEach(([r0, r1, expect]) => {
     t.test(`${r0} <~> ${r1}`, t => {