From 06313d255bb108839fe9691a2ebe7f8043bb303d Mon Sep 17 00:00:00 2001
From: "Charles-P. Clermont" <charles@cpclermont.com>
Date: Mon, 4 Dec 2017 12:13:45 -0500
Subject: [PATCH] Improve indexBy type inference

---
 types/ramda/index.d.ts     |  4 ++--
 types/ramda/ramda-tests.ts | 15 ++++++++++++---
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/types/ramda/index.d.ts b/types/ramda/index.d.ts
index 9d1683fbbc..de4a05b28f 100644
--- a/types/ramda/index.d.ts
+++ b/types/ramda/index.d.ts
@@ -740,8 +740,8 @@ declare namespace R {
          * Given a function that generates a key, turns a list of objects into an object indexing the objects
          * by the given key.
          */
-        indexBy<T, U>(fn: (a: T) => string, list: T[]): U;
-        indexBy<T>(fn: (a: T) => string): <U>(list: T[]) => U;
+        indexBy<T>(fn: (a: T) => string, list: T[]): { [key: string]: T };
+        indexBy<T>(fn: (a: T) => string): (list: T[]) => { [key: string]: T };
 
         /**
          * Returns the position of the first occurrence of an item in an array
diff --git a/types/ramda/ramda-tests.ts b/types/ramda/ramda-tests.ts
index 426bb63471..8e91b12ef2 100644
--- a/types/ramda/ramda-tests.ts
+++ b/types/ramda/ramda-tests.ts
@@ -678,10 +678,19 @@ interface Obj {
 };
 
 (() => {
-    const list = [{id: "xyz", title: "A"}, {id: "abc", title: "B"}];
-    const a1 = R.indexBy(R.prop<string>("id"), list);
-    const a2 = R.indexBy(R.prop<string>("id"))(list);
+    interface Book {
+        id: string;
+        title: string;
+    }
+    const list: Book[] = [{id: "xyz", title: "A"}, {id: "abc", title: "B"}];
+    const a1 = R.indexBy(R.prop("id"), list);
+    const a2 = R.indexBy(R.prop("id"))(list);
     const a3 = R.indexBy<{ id: string }>(R.prop<string>("id"))(list);
+
+    const titlesIndexedByTitles: { [k: string]: string } = R.pipe(
+        R.map((x: Book) => x.title),
+        R.indexBy(x => x),
+    )(list);
 });
 
 () => {