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

1 files changed, 17 insertions, 0 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: