From 61e8e33cd7fdc9a1daee9b5607655729c3df8ce2 Mon Sep 17 00:00:00 2001
From: Junior B <junior@bonto.ch>
Date: Fri, 23 Oct 2015 11:03:39 +0200
Subject: [PATCH] Improves `elementAt` to be platform consistent

---
 .../Observables/Implementations/ElementAt.swift   | 15 +++++++++++++--
 .../Observable+StandardSequenceOperators.swift    |  2 +-
 RxSwift/Rx.swift                                  |  9 +++++++++
 ...Observable+StandardSequenceOperatorsTest.swift |  2 +-
 4 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/RxSwift/Observables/Implementations/ElementAt.swift b/RxSwift/Observables/Implementations/ElementAt.swift
index a5772062..bfc1d8d7 100644
--- a/RxSwift/Observables/Implementations/ElementAt.swift
+++ b/RxSwift/Observables/Implementations/ElementAt.swift
@@ -26,13 +26,24 @@ class ElementAtSink<SourceType, O: ObserverType where O.E == SourceType> : Sink<
         switch event {
         case .Next(_):
 
+            if i < 0 {
+                rxFatalError("index can't be negative")
+            }
+
             if (i == 0) {
                 observer?.on(event)
                 observer?.on(.Completed)
                 self.dispose()
             }
-
-            i--
+            
+            do {
+                try decrementChecked(&i)
+            } catch(let e) {
+                observer?.onError(e)
+                dispose()
+                return
+            }
+            
         case .Error(let e):
             observer?.on(.Error(e))
             self.dispose()
diff --git a/RxSwift/Observables/Observable+StandardSequenceOperators.swift b/RxSwift/Observables/Observable+StandardSequenceOperators.swift
index ffc78908..fadccece 100644
--- a/RxSwift/Observables/Observable+StandardSequenceOperators.swift
+++ b/RxSwift/Observables/Observable+StandardSequenceOperators.swift
@@ -194,6 +194,6 @@ extension ObservableType {
     @warn_unused_result(message="http://git.io/rxs.uo")
     public func elementAt(index: Int)
         -> Observable<E> {
-            return ElementAt(source: self.asObservable(), index: index, throwOnEmpty: false)
+            return ElementAt(source: self.asObservable(), index: index, throwOnEmpty: true)
     }
 }
\ No newline at end of file
diff --git a/RxSwift/Rx.swift b/RxSwift/Rx.swift
index 90598ec3..4621c980 100644
--- a/RxSwift/Rx.swift
+++ b/RxSwift/Rx.swift
@@ -37,6 +37,15 @@ func incrementChecked(inout i: Int) throws -> Int {
     return result
 }
 
+func decrementChecked(inout i: Int) throws -> Int {
+    if i == Int.min {
+        throw RxError.OverflowError
+    }
+    let result = i
+    i -= 1
+    return result
+}
+
 extension NSObject {
     func rx_synchronized<T>(@noescape action: () -> T) -> T {
         objc_sync_enter(self)
diff --git a/RxTests/RxSwiftTests/Tests/Observable+StandardSequenceOperatorsTest.swift b/RxTests/RxSwiftTests/Tests/Observable+StandardSequenceOperatorsTest.swift
index fe9f0b0c..ecdc305c 100644
--- a/RxTests/RxSwiftTests/Tests/Observable+StandardSequenceOperatorsTest.swift
+++ b/RxTests/RxSwiftTests/Tests/Observable+StandardSequenceOperatorsTest.swift
@@ -3708,7 +3708,7 @@ extension ObservableStandardSequenceOperators {
         }
         
         XCTAssertEqual(res.messages, [
-            completed(320)
+            error(320, RxError.ArgumentOutOfRange)
             ])
         
         XCTAssertEqual(xs.subscriptions, [