From 1f20127502e05e5df28d26f8614cb7005dea5b1d Mon Sep 17 00:00:00 2001
From: kahsa <kahsa@moon.gmobb.jp>
Date: Fri, 28 Jan 2022 17:09:52 +0900
Subject: [PATCH] doc: add example for interface casting (#13304)

---
 doc/docs.md | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

diff --git a/doc/docs.md b/doc/docs.md
index 4c9ef7fb4e..7e61550cf4 100644
--- a/doc/docs.md
+++ b/doc/docs.md
@@ -2743,6 +2743,48 @@ fn announce(s Something) {
 	}
 }
 ```
+
+```v
+interface IFoo {
+	foo()
+}
+
+interface IBar {
+	bar()
+}
+
+// implements only IFoo
+struct SFoo {}
+
+fn (sf SFoo) foo() {}
+
+// implements both IFoo and IBar
+struct SFooBar {}
+
+fn (sfb SFooBar) foo() {}
+
+fn (sfb SFooBar) bar() {
+	dump('This implements IBar')
+}
+
+fn main() {
+	mut arr := []IFoo{}
+	arr << SFoo{}
+	arr << SFooBar{}
+
+	for a in arr {
+		dump(a)
+		// In order to execute instances that implements IBar.
+		if a is IBar {
+			// a.bar() // Error.
+			b := a as IBar
+			dump(b)
+			b.bar()
+		}
+	}
+}
+```
+
 For more information, see [Dynamic casts](#dynamic-casts).
 
 #### Interface method definitions