union, intersect, subtract

implementations/javascript/src/flex.ts

@@ -97,7 +97,7 @@ export class FlexMap<K, V> implements Map<K, V> {
         return this.items.values();
     }
 
-    [Symbol.toStringTag] = 'FlexMap';
+    get [Symbol.toStringTag]() { return 'FlexMap'; }
 
     equals(other: any, eqv: Equivalence<V> = (v1, v2) => v1 === v2): boolean {
         if (!('size' in other && 'has' in other && 'get' in other)) return false;
@@ -206,7 +206,7 @@ export class FlexSet<V> implements Set<V> {
         return this.items.values();
     }
 
-    [Symbol.toStringTag] = 'FlexSet';
+    get [Symbol.toStringTag]() { return 'FlexSet'; }
 
     equals(other: any): boolean {
         if (!('size' in other && 'has' in other)) return false;
@@ -220,4 +220,22 @@ export class FlexSet<V> implements Set<V> {
     canonicalValues(): IterableIterator<string> {
         return this.items.keys();
     }
+
+    union(other: Set<V>): FlexSet<V> {
+        const result = new FlexSet(this.canonicalizer, this);
+        for (let k of other) result.add(k);
+        return result;
+    }
+
+    intersect(other: Set<V>): FlexSet<V> {
+        const result = new FlexSet(this.canonicalizer);
+        for (let k of this) if (other.has(k)) result.add(k);
+        return result;
+    }
+
+    subtract(other: Set<V>): FlexSet<V> {
+        const result = new FlexSet(this.canonicalizer);
+        for (let k of this) if (!other.has(k)) result.add(k);
+        return result;
+    }
 }

implementations/javascript/src/values.ts

@@ -598,7 +598,7 @@ export class Dictionary<T> extends FlexMap<Value, T> {
         return this.asPreservesText();
     }
 
-    [Symbol.toStringTag] = 'Dictionary';
+    get [Symbol.toStringTag]() { return 'Dictionary'; }
 
     [PreserveOn](encoder: Encoder) {
         if (encoder.canonical) {
@@ -643,7 +643,7 @@ export class Set extends FlexSet<Value> {
         return new Set(this);
     }
 
-    [Symbol.toStringTag] = 'Set';
+    get [Symbol.toStringTag]() { return 'Set'; }
 
     [PreserveOn](encoder: Encoder) {
         if (encoder.canonical) {