Move if_let syntax to convenience-features section (#4628)

* Move if_let syntax to convenience-features section

* Fix the syntax for setting up an anchor

* update the comment on sample code

* Add example for if_let syntax

* Address the comments

3 files changed, 27 insertions, 5 deletions

diff --git a/docs/user-guide/03-convenience-features.md b/docs/user-guide/03-convenience-features.md
index f4cd51b3f..dc1723ebe 100644
--- a/docs/user-guide/03-convenience-features.md
+++ b/docs/user-guide/03-convenience-features.md
@@ -383,6 +383,23 @@ int caller()
 }
 ```
 
+## `if_let` syntax
+Slang supports `if (let name = expr)` syntax to simplify the code when working with `Optional<T>` value. The syntax is similar to Rust's
+`if let` syntax, the value expression must be an `Optional<T>` type, for example:
+
+```csharp
+Optional<int> getOptInt() { ... }
+
+void test()
+{
+    if (let x = getOptInt())
+    {
+          // if we are here, `getOptInt` returns a value `int`.
+          // and `x` represents the `int` value.
+    }
+}
+```
+
 ## `reinterpret<T>` operation
 
 Sometimes it is useful to reinterpret the bits of one type as another type, for example:
diff --git a/docs/user-guide/06-interfaces-generics.md b/docs/user-guide/06-interfaces-generics.md
index 7935f3551..982b2ba8b 100644
--- a/docs/user-guide/06-interfaces-generics.md
+++ b/docs/user-guide/06-interfaces-generics.md
@@ -677,8 +677,10 @@ T compute<T>(T a1, T a2)
 // compute(3, 1) == 2
 ```
 
-`as` operator can also be used in the `if` predicate to test if an object can be casted to a specific type, once the cast test is successful,
-the object can be used in the `if` block as the casted type without the need to retrieve the `Optional<T>::value` property:
+Since `as` operator returns a `Optional<T>` type, it can also be used in the `if` predicate to test if an object can be
+casted to a specific type, once the cast test is successful, the object can be used in the `if` block as the casted type
+without the need to retrieve the `Optional<T>::value` property, for example:
+
 ```csharp
 interface IFoo
 {
@@ -704,10 +706,10 @@ void test(IFoo foo)
 {
     // This syntax will be desugared to the following:
     // {
-    //      Optional<MyImpl1> $OptVar = foo as MyImpl1;
-    //      if ($OptVar.hasValue)
+    //      Optional<MyImpl1> optVar = foo as MyImpl1;
+    //      if (optVar.hasValue)
     //      {
-    //          MyImpl1 t = $OptVar.value;
+    //          MyImpl1 t = optVar.value;
     //          t.foo();
     //      }
     //      else if ...
@@ -734,6 +736,8 @@ void main()
 }
 
 ```
+See  [if-let syntax](convenience-features.html#if_let-syntax) for more details.
+
 
 Extensions to Interfaces
 -----------------------------
diff --git a/docs/user-guide/toc.html b/docs/user-guide/toc.html
index 2adb7655b..c1915e5dc 100644
--- a/docs/user-guide/toc.html
+++ b/docs/user-guide/toc.html
@@ -39,6 +39,7 @@
 <li data-link="convenience-features#operator-overloading"><span>Operator Overloading</span></li>
 <li data-link="convenience-features#subscript-operator"><span>Subscript Operator</span></li>
 <li data-link="convenience-features#optionalt-type"><span>`Optional&lt;T&gt;` type</span></li>
+<li data-link="convenience-features#if_let-syntax"><span>`if_let` syntax</span></li>
 <li data-link="convenience-features#reinterprett-operation"><span>`reinterpret&lt;T&gt;` operation</span></li>
 <li data-link="convenience-features#pointers-limited"><span>Pointers (limited)</span></li>
 <li data-link="convenience-features#struct-inheritance-limited"><span>`struct` inheritance (limited)</span></li>