# Traits 2
Traits are *like* interfaces, that you can implement on existing types.
```rust ,no_run
fn turn_on_heater<T>(t: T)
where
T: TemperatureExt,
{
if t.is_cold() {
println!("❄️ It's cold, turning on heater");
} else {
println!("🔥 It's not cold, not turning on heater.");
}
}
# fn main() {}
```
```rust ,no_run
#
#
#
#
#
#
#
#
trait TemperatureExt {
fn is_cold(self) -> bool;
}
```
```rust
# fn turn_on_heater<T>(t: T)
# where
# T: TemperatureExt,
# {
# if t.is_cold() {
# println!("❄️ It's cold, turning on heater");
# } else {
# println!("🔥 It's not cold, not turning on heater.");
# }
# }
# trait TemperatureExt {
# fn is_cold(self) -> bool;
# }
fn main() {
turn_on_heater(2);
turn_on_heater("freezing");
turn_on_heater("warm");
// turn_on_heater(Vec::new()); // compile error
}
impl TemperatureExt for i32 {
fn is_cold(self) -> bool {
self < 20
}
}
impl<'s> TemperatureExt for &'s str {
fn is_cold(self) -> bool {
self == "freezing"
}
}
```
