indexedSeq.interpose()

__tests__/interpose.ts

@@ -0,0 +1,34 @@
+///<reference path='../resources/jest.d.ts'/>
+///<reference path='../dist/Immutable.d.ts'/>
+
+jest.autoMockOff();
+
+import I = require('immutable');
+
+describe('interpose', () => {
+
+  it('separates with a value', () => {
+    var range = I.Range(10, 15);
+    var interposed = range.interpose(0);
+    expect(interposed.toArray()).toEqual(
+      [ 10, 0, 11, 0, 12, 0, 13, 0, 14 ]
+    );
+  })
+
+  it('can be iterated', () => {
+    var range = I.Range(10, 15);
+    var interposed = range.interpose(0);
+    var values = interposed.values();
+    expect(values.next()).toEqual({ value: 10, done: false });
+    expect(values.next()).toEqual({ value: 0, done: false });
+    expect(values.next()).toEqual({ value: 11, done: false });
+    expect(values.next()).toEqual({ value: 0, done: false });
+    expect(values.next()).toEqual({ value: 12, done: false });
+    expect(values.next()).toEqual({ value: 0, done: false });
+    expect(values.next()).toEqual({ value: 13, done: false });
+    expect(values.next()).toEqual({ value: 0, done: false });
+    expect(values.next()).toEqual({ value: 14, done: false });
+    expect(values.next()).toEqual({ value: undefined, done: true });
+  })
+
+})

dist/Immutable.d.ts

@@ -975,6 +975,12 @@ declare module 'immutable' {
       context?: any
     ): Sequence<G, any/*IndexedSequence<T>*/>; // Bug: exposing this causes the type checker to implode.
 
+    /**
+     * Returns a lazy sequence with `separator` between each item in this
+     * sequence.
+     */
+    interpose(separator: T): IndexedSequence<T>;
+
     /**
      * Mapper takes IndexedSequence.
      * @override

dist/Immutable.js

@@ -672,6 +672,9 @@ var $IndexedSequence = IndexedSequence;
     index = wrapIndex(this, index);
     return index >= 0 && (this.length != null ? this.length === Infinity || index < this.length : this.indexOf(index) !== -1);
   },
+  interpose: function(separator) {
+    return interposeFactory(this, separator);
+  },
   last: function() {
     return this.get(this.length ? this.length - 1 : 0);
   },
@@ -1485,6 +1488,33 @@ function flattenFactory(sequence, useKeys) {
   };
   return flatSequence;
 }
+function interposeFactory(sequence, separator) {
+  var interposedSequence = sequence.__makeSequence();
+  interposedSequence.length = sequence.length && sequence.length * 2 - 1;
+  interposedSequence.__iterateUncached = function(fn, reverse) {
+    var $__0 = this;
+    var iterations = 0;
+    sequence.__iterate((function(v, k) {
+      return (!iterations || fn(separator, iterations++, $__0) !== false) && fn(v, iterations++, $__0) !== false;
+    }), reverse);
+    return iterations;
+  };
+  interposedSequence.__iteratorUncached = function(type, reverse) {
+    var iterator = sequence.__iterator(ITERATE_VALUES, reverse);
+    var iterations = 0;
+    var step;
+    return new Iterator((function() {
+      if (!step || iterations % 2) {
+        step = iterator.next();
+        if (step.done) {
+          return step;
+        }
+      }
+      return iterations % 2 ? iteratorValue(type, iterations++, separator) : iteratorValue(type, iterations++, step.value, step);
+    }));
+  };
+  return interposedSequence;
+}
 var Cursor = function Cursor(rootData, keyPath, onChange, value) {
   value = value ? value : rootData.getIn(keyPath);
   this.length = value instanceof Sequence ? value.length : null;