Implement pitch.getEnharmonic().

src/pitch.ts

@@ -571,7 +571,7 @@ export class Pitch extends prebase.ProtoM21Object {
         } else {
             this.octave = p.octave;
         }
-        return p;
+        return this;
     }
 
     /**
@@ -591,7 +591,38 @@ export class Pitch extends prebase.ProtoM21Object {
     getLowerEnharmonic(inPlace=false) {
         return this._getEnharmonicHelper(inPlace, -1);
     }
-    /* TODO: isEnharmonic, getEnharmonic, getAllCommonEnharmonics */
+
+    getEnharmonic(inPlace=false): Pitch {
+        let post = this;
+        if (!inPlace) {
+            post = this.clone();
+        }
+
+        if (post.accidental !== undefined) {
+            if (post.accidental.alter > 0) {
+                // we have a sharp, need to get the equivalent flat
+                post.getHigherEnharmonic(true);
+            } else if (post.accidental.alter < 0) {
+                post.getLowerEnharmonic(true);
+            } else {
+                // assume some direction, perhaps using a dictionary
+                if (['C', 'D', 'G'].includes(this.step)) {
+                    post.getLowerEnharmonic(true);
+                } else {
+                    post.getHigherEnharmonic(true);
+                }
+            }
+        } else {
+            if (['C', 'D', 'G'].includes(this.step)) {
+                post.getLowerEnharmonic(true);
+            } else {
+                post.getHigherEnharmonic(true);
+            }
+        }
+
+        return post;
+    }
+    /* TODO: isEnharmonic, getAllCommonEnharmonics */
 
     protected _nameInKeySignature(alteredPitches: Pitch[]) : boolean {
         for (const p of alteredPitches) {  // all are altered tones, must have acc

tests/moduleTests/pitch.ts

@@ -107,7 +107,8 @@ export default function tests() {
         assert.equal(dis.octave, 5, 'Pitch octave set to 5');
 
         // inPlace
-        dis.getHigherEnharmonic(true); // inPlace
+        const same = dis.getHigherEnharmonic(true); // inPlace
+        assert.equal(same, dis, 'inPlace=True returns same object');
         assert.equal(dis.nameWithOctave, es.nameWithOctave);
 
         const cDblSharp = new music21.pitch.Pitch('C##5');
@@ -131,6 +132,32 @@ export default function tests() {
         // assert.equal(bSharp.octave, undefined, 'octave should be undefined');
         // assert.equal(bSharp.name, 'B#');
 
+        // getEnharmonic (not inPlace)
+        const start1 = new music21.pitch.Pitch('E-5');
+        const expectedFirst1 = new music21.pitch.Pitch('D#5');
+        const expectedSecond1 = new music21.pitch.Pitch('E-5');
+
+        const first1 = start1.getEnharmonic();
+        assert.notEqual(first1, start1, 'should not return the same (modified) object');
+        assert.equal(first1.nameWithOctave, expectedFirst1.nameWithOctave);
+
+        const second1 = first1.getEnharmonic();
+        assert.notEqual(second1, first1, 'should not return the same (modified) object');
+        assert.equal(second1.nameWithOctave, expectedSecond1.nameWithOctave);
+
+        // getEnharmonic (inPlace)
+        const start2 = new music21.pitch.Pitch('F-3');
+        const expectedFirst2 = new music21.pitch.Pitch('E3');
+        const expectedSecond2 = new music21.pitch.Pitch('F-3');
+
+        const first2 = start2.getEnharmonic(true);
+        assert.equal(first2, start2, 'should return the same (modified) object');
+        assert.equal(first2.nameWithOctave, expectedFirst2.nameWithOctave);
+
+        const second2 = first2.getEnharmonic(true);
+        assert.equal(second2, first2, 'should return the same (modified) object');
+        assert.equal(second2.nameWithOctave, expectedSecond2.nameWithOctave);
+
     });
 
     test('music21.pitch.Pitch To String', assert => {