patterns/src/idioms/concat-format.md

# Concatenating strings with `format!`

## Description

It is possible to build up strings using the `push` and `push_str` methods on a
mutable `String`, or using its `+` operator. However, it is often more
convenient to use `format!`, especially where there is a mix of literal and
non-literal strings.

## Example

```rust
fn say_hello(name: &str) -> String {
    // We could construct the result string manually.
    // let mut result = "Hello ".to_owned();
    // result.push_str(name);
    // result.push('!');
    // result

    // But using format! is better.
    format!("Hello {}!", name)
}
```

## Advantages

Using `format!` is usually the most succinct and readable way to combine
strings.

## Disadvantages

It is usually not the most efficient way to combine strings - a series of `push`
operations on a mutable string is usually the most efficient (especially if the
string has been pre-allocated to the expected size).