From 111e83c97609fb040debfb75fe9f569ed222a290 Mon Sep 17 00:00:00 2001
From: Steve Sanderson <SteveSandersonMS@users.noreply.github.com>
Date: Wed, 10 Jan 2018 12:31:25 +0000
Subject: [PATCH] Clean up usage of RenderComponentArgs in TS by explicitly
 defining accessors

---
 .../src/Rendering/RenderComponentArgs.ts           | 14 ++++++++++++++
 .../src/Rendering/Renderer.ts                      | 11 ++++++-----
 2 files changed, 20 insertions(+), 5 deletions(-)
 create mode 100644 src/Microsoft.Blazor.Browser.JS/src/Rendering/RenderComponentArgs.ts

diff --git a/src/Microsoft.Blazor.Browser.JS/src/Rendering/RenderComponentArgs.ts b/src/Microsoft.Blazor.Browser.JS/src/Rendering/RenderComponentArgs.ts
new file mode 100644
index 0000000000..5f5cea5485
--- /dev/null
+++ b/src/Microsoft.Blazor.Browser.JS/src/Rendering/RenderComponentArgs.ts
@@ -0,0 +1,14 @@
+import { Pointer, System_Array } from '../Platform/Platform';
+import { platform } from '../Environment';
+
+// Keep in sync with the RenderComponentArgs struct in .NET code
+export const renderComponentArgs = {
+  browserRendererId: (obj: RenderComponentArgsPointer) => platform.readInt32Field(obj, 0),
+  componentId: (obj: RenderComponentArgsPointer) => platform.readInt32Field(obj, 4),
+  renderTree: (obj: RenderComponentArgsPointer) => platform.readObjectField(obj, 8) as System_Array,
+  renderTreeLength: (obj: RenderComponentArgsPointer) => platform.readInt32Field(obj, 12),
+}
+
+// Nominal type to ensure only valid pointers are passed to the renderComponentArgs functions.
+// At runtime the values are just numbers.
+export interface RenderComponentArgsPointer extends Pointer { RenderComponentArgsPointer__DO_NOT_IMPLEMENT: any }
diff --git a/src/Microsoft.Blazor.Browser.JS/src/Rendering/Renderer.ts b/src/Microsoft.Blazor.Browser.JS/src/Rendering/Renderer.ts
index 5d051bb9c0..6988731eed 100644
--- a/src/Microsoft.Blazor.Browser.JS/src/Rendering/Renderer.ts
+++ b/src/Microsoft.Blazor.Browser.JS/src/Rendering/Renderer.ts
@@ -1,6 +1,7 @@
 import { System_Object, System_String, System_Array, MethodHandle, Pointer } from '../Platform/Platform';
 import { platform } from '../Environment';
 import { getTreeNodePtr, renderTreeNode, NodeType, RenderTreeNodePointer } from './RenderTreeNode';
+import { renderComponentArgs, RenderComponentArgsPointer } from './RenderComponentArgs';
 let raiseEventMethod: MethodHandle;
 let renderComponentMethod: MethodHandle;
 
@@ -24,14 +25,14 @@ export function attachComponentToElement(browserRendererId: number, elementSelec
   browserRenderers[browserRendererId][componentId] = element;
 }
 
-export function renderRenderTree(renderComponentArgs: Pointer) {
-  const browserRendererId = platform.readInt32Field(renderComponentArgs, 0);
+export function renderRenderTree(args: RenderComponentArgsPointer) {
+  const browserRendererId = renderComponentArgs.browserRendererId(args);
   const browserRenderer = browserRenderers[browserRendererId];
   if (!browserRenderer) {
     throw new Error(`There is no browser renderer with ID ${browserRendererId}.`);
   }
 
-  const componentId = platform.readInt32Field(renderComponentArgs, 4);
+  const componentId = renderComponentArgs.componentId(args);
   const element = browserRenderer[componentId];
   if (!element) {
     throw new Error(`No element is currently associated with component ${componentId}`);
@@ -39,8 +40,8 @@ export function renderRenderTree(renderComponentArgs: Pointer) {
 
   clearElement(element);
 
-  const tree = platform.readObjectField(renderComponentArgs, 8) as System_Array;
-  const treeLength = platform.readInt32Field(renderComponentArgs, 12);
+  const tree = renderComponentArgs.renderTree(args);
+  const treeLength = renderComponentArgs.renderTreeLength(args);
   insertNodeRange(browserRendererId, componentId, element, tree, 0, treeLength - 1);
 }