Enabled strict null checking

Note this version generates some errors, all of which seem valid to me.  If we adopt this, it seems like it could replace the @NotNull decorator.

src/misc/Array2DHashSet.ts

@@ -51,9 +51,9 @@ const LOAD_FACTOR: number =  0.75;
 
 export class Array2DHashSet<T> implements JavaSet<T> {
 	@NotNull
-	protected comparator: EqualityComparator<T>; 
+	protected comparator: EqualityComparator<T> | null; 
 
-	protected buckets: T[][]; 
+	protected buckets: (T|undefined)[][]; 
 
 	/** How many elements in set */
 	protected n: number =  0;
@@ -65,7 +65,7 @@ export class Array2DHashSet<T> implements JavaSet<T> {
 
 	constructor(
 		 @Nullable 
-		 comparator: EqualityComparator<T> = null, 
+		 comparator: EqualityComparator<T> | null = null, 
 		 initialCapacity: number = INITAL_CAPACITY,
 		 initialBucketCapacity: number = INITAL_BUCKET_CAPACITY)  {
 
@@ -86,7 +86,7 @@ export class Array2DHashSet<T> implements JavaSet<T> {
 
 	protected getOrAddImpl(o: T): T {
 		let b: number =  this.getBucket(o);
-		let bucket: T[] =  this.buckets[b];
+		let bucket = this.buckets[b];
 
 		// NEW BUCKET
 		if ( bucket==null ) {
@@ -99,7 +99,7 @@ export class Array2DHashSet<T> implements JavaSet<T> {
 
 		// LOOK FOR IT IN BUCKET
 		for (let i=0; i<bucket.length; i++) {
-			let existing: T =  bucket[i];
+			let existing =  bucket[i];
 			if ( existing==null ) { // empty slot; not there, add.
 				bucket[i] = o;
 				this.n++;
@@ -116,10 +116,10 @@ export class Array2DHashSet<T> implements JavaSet<T> {
 		return o;
 	}
 
-	get(o: T): T {
+	get(o: T): T | null {
 		if ( o==null ) return o;
-		let b: number =  this.getBucket(o);
-		let bucket: T[] =  this.buckets[b];
+		let b: number = this.getBucket(o);
+		let bucket = this.buckets[b];
 		if ( bucket==null ) return null; // no bucket
 		for (let e of bucket) {
 			if ( e==null ) return null; // empty slot; not there
@@ -159,7 +159,7 @@ export class Array2DHashSet<T> implements JavaSet<T> {
 	}
 
 	protected expand(): void {
-		let old: T[][] =  this.buckets;
+		let old = this.buckets;
 		this.currentPrime += 4;
 		let newCapacity: number =  this.buckets.length * 2;
 		let newTable: T[][] =  this.createBuckets(newCapacity);
@@ -273,14 +273,14 @@ export class Array2DHashSet<T> implements JavaSet<T> {
 		}
 
 		let b: number =  this.getBucket(obj);
-		let bucket: T[] =  this.buckets[b];
+		let bucket: (T|undefined)[] =  this.buckets[b];
 		if ( bucket==null ) {
 			// no bucket
 			return false;
 		}
 
 		for (let i=0; i<bucket.length; i++) {
-			let e: T =  bucket[i];
+			let e: T | undefined =  bucket[i];
 			if ( e==null ) {
 				// empty slot; not there
 				return false;

src/misc/Stubs.ts

@@ -148,7 +148,10 @@ class IterableAdapter<T> implements Iterable<T>, IterableIterator<T> {
     [Symbol.iterator]() { this._iterator = this.collection.iterator(); return this;}
 
     next(): IteratorResult<T> {
-        if (!this._iterator.hasNext()) return { done: true, value: undefined };
+        if (!this._iterator.hasNext()) {
+            // A bit of a hack needed here, tracking under https://github.com/Microsoft/TypeScript/issues/11375
+            return { done: true, value: undefined } as any as IteratorResult<T>;
+        }
         return {done: false, value: this._iterator.next()}
     }
 }

tsconfig.json

@@ -5,6 +5,7 @@
     "module": "commonjs",
     "target": "es2015",
     "noImplicitAny": true,
+    "strictNullChecks": true,
     "experimentalDecorators": true,
     "declaration": true,
     "preserveConstEnums": true,