From d62fbf04fec0cbe7f9bdae70555c342430c3da00 Mon Sep 17 00:00:00 2001
From: Tetsuharu OHZEKI <saneyuki.snyk@gmail.com>
Date: Mon, 12 Sep 2016 13:06:01 +0900
Subject: [PATCH 1/4] feat(filter): Observable<T>.filter() can take type guard
 as the predicate function

---
 src/operator/filter.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/operator/filter.ts b/src/operator/filter.ts
index 980a91b380..7a4958926c 100644
--- a/src/operator/filter.ts
+++ b/src/operator/filter.ts
@@ -50,6 +50,7 @@ export function filter<T>(predicate: (value: T, index: number) => boolean,
 
 export interface FilterSignature<T> {
   (predicate: (value: T, index: number) => boolean, thisArg?: any): Observable<T>;
+  <S extends T>(predicate: (value: T, index: number) => value is S, thisArg?: any): Observable<S>;
 }
 
 class FilterOperator<T> implements Operator<T, T> {

From b952718d35ddda77124a043afbe0a7832620fe3b Mon Sep 17 00:00:00 2001
From: Tetsuharu OHZEKI <saneyuki.snyk@gmail.com>
Date: Wed, 14 Sep 2016 14:02:00 +0900
Subject: [PATCH 2/4] feat(find): Observable<T>.find() can take type guard as
 the predicate function

---
 src/operator/find.ts | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/operator/find.ts b/src/operator/find.ts
index 5d475bb6d1..3d99ed59a4 100644
--- a/src/operator/find.ts
+++ b/src/operator/find.ts
@@ -45,6 +45,7 @@ export function find<T>(predicate: (value: T, index: number, source: Observable<
 
 export interface FindSignature<T> {
   (predicate: (value: T, index: number, source: Observable<T>) => boolean, thisArg?: any): Observable<T>;
+  <S extends T>(predicate: (value: T, index: number, source: Observable<T>) => value is S, thisArg?: any): Observable<S>;
 }
 
 export class FindValueOperator<T> implements Operator<T, T> {

From f99ca49a30287d73bca3cb063ab73b191dcedf26 Mon Sep 17 00:00:00 2001
From: Tetsuharu OHZEKI <saneyuki.snyk@gmail.com>
Date: Wed, 14 Sep 2016 14:04:39 +0900
Subject: [PATCH 3/4] feat(first): Observable<T>.first() can take type guard as
 the predicate function

---
 src/operator/first.ts | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/operator/first.ts b/src/operator/first.ts
index f1cd6825c3..f07486e679 100644
--- a/src/operator/first.ts
+++ b/src/operator/first.ts
@@ -58,9 +58,15 @@ export function first<T, R>(predicate?: (value: T, index: number, source: Observ
   return this.lift(new FirstOperator(predicate, resultSelector, defaultValue, this));
 }
 
+// We can cast `T -> R` in it if we pass the result selector.
+// Therefore we don't provide the signature which takes both a type guard function
+// as the predicate and the result selector.
+// (see #1936)
 export interface FirstSignature<T> {
   (predicate?: (value: T, index: number, source: Observable<T>) => boolean): Observable<T>;
+  <S extends T>(predicate?: (value: T, index: number, source: Observable<T>) => value is S): Observable<S>;
   (predicate: (value: T, index: number, source: Observable<T>) => boolean, resultSelector: void, defaultValue?: T): Observable<T>;
+  <S extends T>(predicate: (value: T, index: number, source: Observable<T>) => value is S, resultSelector: void, defaultValue?: S): Observable<S>;
   <R>(predicate?: (value: T, index: number, source: Observable<T>) => boolean, resultSelector?: (value: T, index: number) => R,
       defaultValue?: R): Observable<R>;
 }

From 76a8a5743948266ef0af8d1833a790d2448ad99f Mon Sep 17 00:00:00 2001
From: Tetsuharu OHZEKI <saneyuki.snyk@gmail.com>
Date: Wed, 14 Sep 2016 14:14:33 +0900
Subject: [PATCH 4/4] feat(last): Observable<T>.last() can take type guard as
 the predicate function

---
 src/operator/last.ts | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/operator/last.ts b/src/operator/last.ts
index 84dafdc2e2..a7b639ca1c 100644
--- a/src/operator/last.ts
+++ b/src/operator/last.ts
@@ -26,9 +26,15 @@ export function last<T, R>(predicate?: (value: T, index: number, source: Observa
   return this.lift(new LastOperator(predicate, resultSelector, defaultValue, this));
 }
 
+// We can cast `T -> R` in it if we pass the result selector.
+// Therefore we don't provide the signature which takes both a type guard function
+// as the predicate and the result selector.
+// (see #1936)
 export interface LastSignature<T> {
   (predicate?: (value: T, index: number, source: Observable<T>) => boolean): Observable<T>;
+  <S extends T>(predicate?: (value: T, index: number, source: Observable<T>) => value is S): Observable<S>;
   (predicate: (value: T, index: number, source: Observable<T>) => boolean, resultSelector: void, defaultValue?: T): Observable<T>;
+  <S extends T>(predicate: (value: T, index: number, source: Observable<T>) => value is S, resultSelector: void, defaultValue?: S): Observable<S>;
   <R>(predicate?: (value: T, index: number, source: Observable<T>) => boolean, resultSelector?: (value: T, index: number) => R,
       defaultValue?: R): Observable<R>;
 }