Blanket Trait Implementations

We can use a generic impl block to implement a trait for multiple types at once, generally based on the behavior provided by another trait. These are referred to as blanket implementations.

// Copyright 2025 Google LLC
// SPDX-License-Identifier: Apache-2.0

pub trait PrettyPrint {
    fn pretty_print(&self);
}

// A blanket implementation! If something implements Display, it implements
// PrettyPrint.
impl<T> PrettyPrint for T
where
    T: std::fmt::Display,
{
    fn pretty_print(&self) {
        println!("{self}")
    }
}

impl blocks can be generic, which allow us to apply an implementation to multiple types at once. This is commonly used when applying an impl block to a generic type, but can also be used to implement a trait for multiple types at once.
When an impl block applies to multiple types, we refer this as a “blanket impl”.
In the example above we have a blanket implementation for all types that implement Display.
Blanket impls can restrict how traits are implemented. Rust prevents a type from implementing the same trait twice, so a blanket impl prevents the trait from being implemented directly on a covered type.
- Demonstrate this by adding an implementation for String and show the resulting error.
- Avoid a blanket impl if users are likely to want to customize the behavior of the implementation beyond what the blanket impl provides.

ref:

https://doc.rust-lang.org/reference/glossary.html#blanket-implementation

Keyboard shortcuts

Comprehensive Rust 🦀

Blanket Trait Implementations