06: include closures_fun sample

Author: wprzytula

content/lessons/06_closures_iterators/closures_fun.rs

@@ -40,6 +40,7 @@ fn main() {
         // So, for FnOnce, we need to be their owners to be able to call them,
         // and we can't have a `dyn` object owned on stack.
         // We will solve this problem soon with smart pointers (e.g., Box).
+        // This will give us `std::function` -like experience.
     }
 
     // Mutable reference to FnMut is required to be able to call it.

content/lessons/06_closures_iterators/index.md

@@ -46,10 +46,17 @@ Those traits and the `fn` type form a hierarchy: `fn` ⊆  `Fn` ⊆ `FnMut` ⊆
 
 <!--> $$ fn \subseteq Fn \subseteq FnMut \subseteq FnOnce $$ -->
 
-The following code sample demonstrates various ways to capture environment (borrowing or moving) and various 
+The following code sample demonstrates various ways to capture environment (borrowing or moving) and various kinds of closures, based on what they do with their captures:
 
 {{ include_code_sample(path="lessons/06_closures_iterators/closures_capturing.rs", language="rust") }}
 
+### Closures as trait objects (in dynamic dispatch)
+
+The following code sample shows how one can use closures as `dyn Trait` objects, bypassing the problem of them having anonymous types:
+
+{{ include_code_sample(path="lessons/06_closures_iterators/closures_fun.rs", language="rust") }}
+
+
 ## Examples
 
 We'll go through the examples from [Rust by Example](https://doc.rust-lang.org/rust-by-example/fn/closures.html).