diff --git a/LayoutLink.js b/LayoutLink.js
index 2e0d4e1..ac0ae98 100644
--- a/LayoutLink.js
+++ b/LayoutLink.js
@@ -117,12 +117,7 @@ class LayoutLink {
     }
 
     for (let hop of this.path) {
-      let links = this.linksByPos_.get(hop);
-      if (!links) {
-        links = [];
-        this.linksByPos_.set(hop, links);
-      }
-      links.push(this);
+      getOrSet(this.linksByPos_, hop, []).push(this);
     }
 
     console.log(iter);
diff --git a/StringMap.js b/StringMap.js
new file mode 100644
index 0000000..fee2aaa
--- /dev/null
+++ b/StringMap.js
@@ -0,0 +1,17 @@
+class StringMap extends Map {
+  has(key) {
+    return super.has(key.toString());
+  }
+
+  get(key) {
+    return super.get(key.toString());
+  }
+
+  set(key, value) {
+    return super.set(key.toString(), value);
+  }
+
+  delete(key) {
+    return super.delete(key.toString());
+  }
+}
diff --git a/utils.js b/utils.js
index 5643919..d047682 100644
--- a/utils.js
+++ b/utils.js
@@ -25,20 +25,4 @@ function intersects(set1, set2) {
   return false;
 }
 
-class StringMap extends Map {
-  has(key) {
-    return super.has(key.toString());
-  }
-
-  get(key) {
-    return super.get(key.toString());
-  }
-
-  set(key, value) {
-    return super.set(key.toString(), value);
-  }
-
-  delete(key) {
-    return super.delete(key.toString());
-  }
-}
+<!--# include file="StringMap.js" -->