Crate io_providers [] [src]

Defines "provider" traits and implementations for different types of I/O operations.

The purpose of this is mainly for dependency injection: by having your code depend on a generic provider, it can be tested by giving it a virtual, inspectable implementation of that provider. In production, the "real" implementation can be used.

Each type of provider exists in its own submodule and can be used independently. However, this module also contains the all-encompassing IoProvider trait which provides access to all of them. If you have a lot of I/O dependencies, it might be easier to create and pass around one &mut IoProvider rather than several different providers.


extern crate io_providers;

use std::io::Write;
use std::path::Path;
use io_providers::{IoProvider, LocalIoProvider, VirtualIoProvider};
use io_providers::env::Provider as EnvProvider;
use io_providers::stream::Provider as StreamProvider;

/// Gets the current working directory and prints it to stdout.
fn do_work<P: IoProvider>(io: &mut P) {
    let cur_dir = io.env().current_dir().unwrap();
    let stdout =;
    writeln!(stdout, "The current directory is: {}", cur_dir.to_str().unwrap()).unwrap();

fn main() {

    // Use a local I/O provider here to get real interaction with the system
    let mut io = LocalIoProvider::new();
    do_work(&mut io);

fn test_do_work_prints_current_dir() {
    // Use a virtual I/O provider here so we can verify how it was used
    let mut virtual_io = VirtualIoProvider::new();

    do_work(&mut virtual_io);

        "The current directory is: /foo/bar\n",



Providers of environment data, such as the working directory and environment variables.


Providers of input/output/error streams (i.e. stdin, stdout and stderr).



"Real" implementer of IoProvider, using standard streams and the local environment.


Virtual implementer of IoProvider, using in-memory data which can be inspected.



Provides access to an environment provider and a stream provider.