3.1.13 The nameof operator

chap03.md

@@ -309,7 +309,67 @@ class Class1
 
 Details of Finalizer is in Chap12
 
-### 3.1.12 The `nameof` operator
+### 3.1.12 Partial Types and Methods
+
+**Partial Types** (e.g. partial class, partial struct) allow definition to be split into multiple files.
+* e.g. a partial class is autogenerated using template; that class is enhanced with hand-authored content in another file
+
+Syntax Required:
+* Each participant (i.e. partial types) require `partial` declaration
+* All participants cannot have conflicting member (i.e. same paramter, same return)
+* Partial types are resolved at compile time.
+
+e.g. partial type in different files
+```csharp
+// auto-generated file - PaymentFormGen.cs
+partial class PaymentForm {...}
+
+// hand-authored - PaymentForm.cs
+partial class PaymentForm {...}
+```
+
+#### Partial methods
+
+A partial type can contain **partial methods**. So autogenerated partial type can provide customizable hooks for manual change
+
+Syntax of partial methods:
+* consists of 2 part: a *definition* (in auto-generated file) and an *implementation* (in hand-authored file)
+* If implementation is not provided, definition of the partial method is compiled anyway.
+* Partial methods is `void`, and implicitly `private`, cannot include `out` parameter
+
+```csharp
+// In auto-generated file e.g. PartialFileGen.cs
+partial class PaymentForm
+{
+    ...
+    partial void ValidatePayment(decimal amount); // Definition
+}
+
+// In hand-authored file
+partial class PaymentForm
+{
+    ...
+    partial void ValidatePayment(decimal amount) // implementation
+    {
+        if (amount > 100)
+        ...
+    }
+}
+```
+
+#### Extended partial methods (C# 9)
+
+TODO: Omit
+
+### 3.1.13 The `nameof` operator
+
+* `nameof` operator returns name of any symbol (type, memeber, variable, etc.) as a string
+* Advantage of `nameof`: static type checking, e.g. if rename the symbol, all references will be renamed
+
+```csharp
+int count = 123;
+string name = nameof(count); // name is "count"
+```
 
 ## 3.2 Inheritance