diff --git a/src/codelens/codeLensProvider.ts b/src/codelens/codeLensProvider.ts
index 02c22ac..bb258ea 100644
--- a/src/codelens/codeLensProvider.ts
+++ b/src/codelens/codeLensProvider.ts
@@ -681,5 +681,5 @@ function getRangeFromSymbol(symbol: DocumentSymbol | SymbolInformation) {
 }
 
 function isDocumentSymbol(symbol: DocumentSymbol | SymbolInformation): symbol is DocumentSymbol {
-    return (symbol as DocumentSymbol).children !== undefined;
+    return Functions.is<DocumentSymbol>(symbol, 'children');
 }
diff --git a/src/system/function.ts b/src/system/function.ts
index 1dbabb4..a1d7147 100644
--- a/src/system/function.ts
+++ b/src/system/function.ts
@@ -119,6 +119,20 @@ export namespace Functions {
             : [];
     }
 
+    export function is<T extends object>(o: object, prop: keyof T, value?: any): o is T;
+    export function is<T extends object>(o: object, matcher: (o: object) => boolean): o is T;
+    export function is<T extends object>(
+        o: object,
+        propOrMatcher: keyof T | ((o: any) => boolean),
+        value?: any
+    ): o is T {
+        if (typeof propOrMatcher === 'function') {
+            return propOrMatcher(o);
+        }
+
+        return value === undefined ? (o as any)[propOrMatcher] !== undefined : (o as any)[propOrMatcher] === value;
+    }
+
     export function isPromise<T>(obj: T | Promise<T>): obj is Promise<T> {
         return obj && typeof (obj as Promise<T>).then === 'function';
     }
diff --git a/src/views/nodes/viewNode.ts b/src/views/nodes/viewNode.ts
index 08a7b0b..4951f45 100644
--- a/src/views/nodes/viewNode.ts
+++ b/src/views/nodes/viewNode.ts
@@ -2,7 +2,7 @@
 import { Command, Disposable, Event, TreeItem, TreeItemCollapsibleState, TreeViewVisibilityChangeEvent } from 'vscode';
 import { GitUri } from '../../git/gitService';
 import { Logger } from '../../logger';
-import { debug, gate, logName } from '../../system';
+import { debug, Functions, gate, logName } from '../../system';
 import { TreeViewNodeStateChangeEvent, View } from '../viewBase';
 
 export enum ResourceType {
@@ -118,16 +118,16 @@ export interface PageableViewNode {
     maxCount: number | undefined;
 }
 
-export function isPageable(
-    node: ViewNode
-): node is ViewNode & { supportsPaging: boolean; maxCount: number | undefined } {
-    return Boolean((node as ViewNode & { supportsPaging: boolean }).supportsPaging);
+export function isPageable(node: ViewNode): node is ViewNode & PageableViewNode {
+    return Functions.is<ViewNode & PageableViewNode>(node, 'supportsPaging', true);
 }
 
-export function supportsAutoRefresh(
-    view: View
-): view is View & { autoRefresh: boolean; onDidChangeAutoRefresh: Event<void> } {
-    return (view as View & { onDidChangeAutoRefresh: Event<void> }).onDidChangeAutoRefresh !== undefined;
+interface AutoRefreshableView {
+    autoRefresh: boolean;
+    onDidChangeAutoRefresh: Event<void>;
+}
+export function supportsAutoRefresh(view: View): view is View & AutoRefreshableView {
+    return Functions.is<View & AutoRefreshableView>(view, 'onDidChangeAutoRefresh');
 }
 
 export abstract class SubscribeableViewNode<TView extends View = View> extends ViewNode<TView> {