easy-shortcuts

Conveniences for Small Programs

Small programs which are meant to play nicely with other system commands need to quit early and return a non-zero exit code. Panicking comes across as untidy in such cases - it's a developer feature.

Consider a program that needs to read all of a file specified on the command line.

use std::io::prelude::*;
use std::fs::File;
use std::env;

let file = env::args().nth(1).expect("please supply a file name");

let mut f = File::open(&file).expect("can't open the file");
let mut s = String::new();
f.read_to_string(&mut s)).expect("can't read the string");

This is a little tedious if you just want to quit.

extern crate easy_shortcuts as es;

let file = es::argn_err(1,"please supply a file name");
let s = es::read_to_string(&file);

And passing a dud filename to this program gives us a clear fatal error:

./read_all error: open 'bonzo.txt' No such file or directory (os error 2)

Other than commands, there's another important category of small programs: little bits of code you write when exploring an API. It's irritating to have to write boilerplate when all you want to do is play with the contents of a file.

Another common need is to iterate over all the lines in a file:

extern crate easy_shortcuts as es:
use std::io;

for line in es::lines(io.stdin()) {
	// do your thang!
}

This creates the io::BufReader and cuts through the Java-esque ceremony to get an iterator over all the lines of a file as strings; it will quit if there's an I/O error while iterating.

Iterator Shortcuts

Sometimes all you want to do is consume an iterator and print out its values. This little snippet will just echo the first ten lines of stdin to stdout:

use es::traits::*;

es::lines(io.stdin()).take(10).print("\n")

Here's a semi-useful example. Unix configuration files often have a large amount of commented out options; this only prints out the options in force:

let conf = es::argn_err(1,"please provide a conf file");
es::lines(es::open(&conf))
    .filter(|s| s.len() > 0 && ! s.starts_with("#"))
    .print("\n");

And there's an equivalent debug which is extremely useful for finding out what an iterator is actually pumping out:

(0..5).map(|n| (n,2*n)).debug("\n");
//->
(0, 0)
(1, 2)
(2, 4)
(3, 6)
(4, 8)

String methods like skip_whitespace return iterators, and easy_shortcuts presents some conveniences for processing and collecting strings:

let strs = ["one","two","three"];
let s = strs.into_iter().prepend(" hello ");
assert_eq!(s," hello one hello two hello three ");

And that old favourite of Pythonistas, join. (It's defined on vectors of strings but as an iterator method we avoid unnecessary creation of temporaries.)

let s = "one two three".split_whitespace().join(',');
assert_eq!(s,"one,two,three");

collect Considered Irritating

There are convenient to_vec and to_map methods available for iterators. collect is very general, and its implementation is trivial: anything that implements the FromIterator trait. Usually you have to give some type hints (the Rust compiler is not psychic yet) but nine times out of ten you want a Vec.

let v: Vec<_> = (0..5).collect();
// easier to read and totally equivalent
let v = (0..5).to_vec();

Here is a quick way to read a config file where keys and values are separated by '=`'

	let map = es::lines(es::open(&conf))
      .filter(|s| ! s.starts_with("#")) // ignore commments
      .filter_map(|s| s.split_at_delim('=').trim()) // split into (String,String)
	  .to_map();

Extra String Goodies

I could not resist adding a few convenient string methods.

split_at_delim is like a combination of the string find and split_at methods, except that the delimiter is not included; "one = two".split_at_delim('=') gives Some(("one "," two")). trim works on the result of this function, converting Option<(&str,&str)> to Option<(String,String)> with any spare whitespace trimmed, or just passes through None.

In the config file example, note that blank lines will be automatically ignored, since split_at_delim will be None, which trim passes through.

Another convenience is is_whitespace defined on strings. This example counts source lines and comment lines, assuming that comments are just '//'.

extern crate easy_shortcuts as es;
use es::traits::*;

fn main() {
	let file = es::argn_err(1,"please provide a source file");
	let mut scount = 0;
	let mut ccount = 0;
	for line in es::lines(es::open(&file)) {
		if let Some(idx) = line.find("//") {
			// now look at everything up to //
			let start = &line[0..idx];
			if start.is_whitespace() {
				ccount += 1;
			}
		}
		scount += 1;	
	}
	println!("source lines {} comment lines {}",scount-ccount,ccount);
}

The preferred solution would be to use a regexp, but Rust's string handling is pretty good on its own - string slices are a lovely feature.

Functions that work on Option<T> or Result<T,E> are very convenient. For instance, the MetadataLike trait adds the boolean methods of fs::Metadata. The reasoning is that usually you'd like to know if a dir entry exists and it is of the desired type.

let ok = fs::metadata(".").is_dir();

// which is short for:
let ok = match fs::metadata(".") {
	Ok(m) => m.is_dir(),
	Err(e) => false
}

Directory Traversal

It is common to need to look at directory contents - the existing API is a little clumsy, especially if you have a "quit early" policy in place. paths provides an iterator over a directory giving a tuple of the path and associated metadata.

extern crate easy_shortcuts as es;

fn has_extension(p: &std::path::Path, e: &str) -> bool {
	match p.extension() {
		Some(ext) => ext == e,
		None => false
	}
}

fn main() {
	for (path,data) in es::paths(".") {
		if data.is_file() && has_extension(&path,"rs") {
			println!("file {:?} len {}",path,data.len());
		}
	}
}

Examples

run-test.rs is a small but non-trivial program using this crate which I wrote to help me write doc tests. Because (to be honest) it's an annoying process; you put code in comments, losing all those lovely visual clues from syntax highlighting, and testing involves a full crate compile plus all those little crates generated by the doc tests. With this little tool I could go from 20s to 0.5s writing doc snippets.

For this workflow, create a subdirectory in the crate directory (I just call it scratch and add to .gitignore). The source file follows the same rules as doc tests themselves, extern crate THIS_CRATE is prepended and a main function created. It compiles and runs the massaged code by copying it to the examples directory and invoking cargo run --example on it.

~/rust/easy-shortcuts/scratch$ cat one.rs
let s = easy_shortcuts::read_to_string("one.rs");
println!("{}",s);
~/rust/easy-shortcuts/scratch$ run-test one.rs

let s = easy_shortcuts::read_to_string("one.rs");
println!("{}",s);


/// ```
/// let s = easy_shortcuts::read_to_string("one.rs");
/// println!("{}",s);
/// ```

We then write out the snippet with the appropriate doc comments. If you run with an extra '!' argument, then module doc comments are created (using //!).

The next useful little program is crate.rs: given a crate name, it will look in Cargo's source cache and print out the source directory of the highest version of that crate.

~/rust/easy-shortcuts/examples$ cargo run -q --example crate semver
/home/steve/.cargo/registry/src/github.com-1ecc6299db9ec823/semver-0.2.3

It would require modification to work on Windows, and if it were a 'real' program it would bring in dependencies on semver, glob, and maybe regex. But it is not meant as an example of good Rust application style, but an example of using easy_shortcuts.