FlatString

A FlatString is a string that is stored in a fixed-size / flat array of characters. This is useful for scenarios where you want to avoid dynamic memory allocation, or where you want to store a string in a fixed-size buffer. A FlatString is a simple struct that contains:

a fixed-size array of type u8
the length of the string
the number of characters.

The maximum store capacity of the FlatString is limited to 255 bytes (so a string has to be less than 255 characters long). As such, the length of the string (in bytes) and the number of characters are stored as a u8 as well.

For example, a FlatString<14> will have a size of 16 bytes (14 bytes for the string, 1 byte for the length, and 1 byte for the number of characters).

Usage

To use a FlatString, you need to add the following to your Cargo.toml:

[dependencies]
flat_string = "1.0.0"

Then, you can use the FlatString as follows:

use flat_string::FlatString;

fn main() {
    // the flat string will be created on the stack
    let s = FlatString::<14>::from_str("Hello World !");
    println!("{}", s);
}

Methods

The following methods are available for the FlatString:

Method	Description
`from_str`	Create a `FlatString` from a string slice
`new`	Create an empty `FlatString`
`len`	Get the length of the string
`is_empty`	Check if the string is empty
`chars_count`	Get the number of characters in the string
`capacity`	Get the capacity of the string
`as_str`	Get the string as a `&str`
`clear`	Clear the string
`push_str`	Ads a string slice to the existig string. If the resulted string size is bigger than the string capacity, the string will be truncated to fit in the allocated capacty.
`push`	Adds a character to the existing string. If the resulted string size is bigger than the string capacity, the string will be truncated to fit in the allocated capacty.
`try_push_str`	Ads a string slice to the existig string only if the resulted string fits in the preallocated capacity. In this case this method will return `Some(&str)` otherwise it returns `None`
`try_push`	Adds a character to the existing string only if the resulted string fits in the preallocated capacity. In this case this method will return `Some(&str)` otherwise it returns `None`
`set`	Set the string to a new value. If the new string size is bigger than the string capacity, the string will be truncated to fit in the allocated capacty.

FlatString implements the following traits:

std::fmt::Display and std::fmt::Debug (this allows you to print the string using println! and dbg!)
std::ops::Deref (this allows you to use the * operator to get the string as a &str). This will also allow you to use the FlatString as a &str in function arguments.
Copy and Clone (this allows you to copy the FlatString using the Copy trait)
PartialEq and Eq (this allows you to compare two FlatString using the == operator)
PartialOrd and Ord (this allows you to compare two FlatString using the <, >, <=, and >= operators)
Default (this allows you to create an empty FlatString)

Example

Create a FlatString from a string slice:

let s = FlatString::<14>::from_str("Hello World !");
// s will be "Hello World !"

Create a FlatString from a string slice that is larger than its capacity:

let s = FlatString::<10>::from_str("Hello World !");
// s will be "Hello Worl" (truncated to fit 10 bytes)

Add a &str to an existing FlatString :

let mut s = FlatString::<30>::from_str("Hello");
// s is "Hello"
s.push_str(" World !");
// s is "Hello World !"

Add a &str to an existing FlatString and exceed the capacity:

let mut s = FlatString::<8>::from_str("Hello");
// s is "Hello"
s.push_str(" World !");
// s is "Hello Wo" (truncated to fit 8 bytes)

Add a &str to an existing FlatString using try_push_str:

let mut s = FlatString::<8>::new();
if let Some(res) = s.try_push_str("Hello") {
    // res is "Hello"
    println!("{}", res);
} else {
    // the string was not added
}
let result = s.try_push_str(" World !") {
// result is None as adding " World !" would exceed the capacity
// s remains "Hello"

Validating the size of a FlatString

 let mut s = FlatString::<8>::new();
 assert_eq!(std::mem::size_of_val(&s), 10);
 // the size of the FlatString is 10 bytes:
 // - 8 bytes for the string
 // - 1 byte for the length
 // - 1 byte for the number of characters

flat_string 1.0.0

FlatString

Usage

Methods

Example