100 exercises to learn Rust

book/src/06_ticket_management/09_impl_trait_2.md

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+# `impl Trait` in argument position
+
+In the previous section, we saw how `impl Trait` can be used to return a type without specifying its name.  
+The same syntax can also be used in **argument position**:
+
+```rust
+fn print_iter(iter: impl Iterator<Item = i32>) {
+    for i in iter {
+        println!("{}", i);
+    }
+}
+```
+
+`print_iter` takes an iterator of `i32`s and prints each element.  
+When used in **argument position**, `impl Trait` is equivalent to a generic parameter with a trait bound:
+
+```rust
+fn print_iter<T>(iter: T) 
+where
+    T: Iterator<Item = i32>
+{
+    for i in iter {
+        println!("{}", i);
+    }
+}
+```
+
+## Downsides
+
+As a rule of thumb, prefer generics over `impl Trait` in argument position.  
+Generics allow the caller to explicitly specify the type of the argument, using the turbofish syntax (`::<>`), 
+which can be useful for disambiguation. That's not the case with `impl Trait`.