Ergonomic, garbage collected strings for Rust
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src fix documentation Mar 17, 2017


Ergonomic, garbage collected strings for Rust.

EZString is similar to the strings in high level languages such as Python and Java. It is designed to be as easy to use as possible by always returning owned values, using reference counting and copy-on-write under the hood in order to make this efficient.

Getting Started

easy_strings is available on Add the following dependency to your Cargo manifest.

easy_strings = "0.2"

Then import it in your code.

extern crate easy_strings;
use easy_strings::{EZString, ez};


The most common way to create an EZString is from a string literal, using the ez() helper function. This interns the string so that calling it multiple times with the same string literal won't result in multiple copies or allocations. (It still requires locking and querying the interned string table each time.)

use easy_strings::{ez};
let s = ez("Hello, world!");

You can also create EZString from existing Strings or &strs.

use easy_strings::{EZString};
let s = EZString::from("foo");
let s = EZString::from("foo".to_string());


To concatenate strings, write &a + &b. This syntax works regardless of the types of a and b, whether they are EZString, &EZString, String, &String, or &str, as long as either a or b is an EZString or &EZString.

let e = ez("E");
let re = &e;
let s = "s".to_string();
let rs = &s;
let lit = "lit";
assert_eq!(&e + &e, "EE");
assert_eq!(&e + &re, "EE");
assert_eq!(&e + &s, "Es");
assert_eq!(&e + &rs, "Es");
assert_eq!(&e + &lit, "Elit");
assert_eq!(&lit + &e, "litE");
assert_eq!(&lit + &re, "litE");
assert_eq!(&s + &re, "sE");
assert_eq!(&rs + &e, "sE");

Note: If you're using Clippy, you should #[allow(needless_borrow)] or you'll get a lot of warnings.

You can also concatenate multiple strings this way, as long as at least one of the first two is EZString or &EZString.

assert_eq!(&lit + &re + &s + &e + &e + &rs, "litEsEEs");

You can also use the += operator. This is optimized to only copy the left hand string when it is not uniquely owned. This means that the following loop is O(n) rather than O(n^2 ) and there is no need for a seperate StringBuilder type like there is in Java.

let mut s = ez("Some numbers: ");
for i in 0..5 {
    s += &i.to_string();
    s += &", ";
assert_eq!(s, "Some numbers: 0, 1, 2, 3, 4, ");


Slicing is done via the substr() method. Note that the indices are by byte, not code point. If the provided indices are not on a code point boundary, substr() will panic.

let mut a = ez("Hello, world!");
assert_eq!(a.substr(1..), "ello, world!");
assert_eq!(a.substr(..6), "Hello,");
assert_eq!(a.substr(1..6), "ello,");
assert_eq!(a.substr(1..a.len()-1), "ello, world");

let b = a.substr(1..3);
a += &b; // b is a copy, so we can freely mutate a

substr() returns the substring as a new EZString. If you want a borrowed slice instead, you can use []. This avoids the extra copy and allocation, at the expense of forcing you to worry about lifetimes, which easy_strings was designed to avoid.

let b = &a[1..3];
assert_eq!(b, "el");
// a += &b; // compile error because b borrowed a


Equality testing between multiple EZStrings or &EZStrings just works. If you want to compare to a String or &str, the EZString should be on the left. If it is on the right, you'll have to prefix it with * (or ** for &EZString).

let e = ez("AAA");
let er = &e;
let s = String::from("AAA");
let sr = &s;
let lit = "AAA";
assert!(e == e);
assert!(er == er);
assert!(e == er);
assert!(er == e);
assert!(e == s);
assert!(e == sr);
assert!(e == lit);
assert!(er == s);
assert!(er == sr);
assert!(er == lit);
assert!(s == *e);
assert!(*sr == *e);
assert!(lit == *e);
assert!(s == **er);
assert!(*sr == **er);
assert!(lit == **er);


EZString is not Copy, which means you must clone it whenever you want to reuse it by value. To work around this, it is recommended that your functions always take EZString parameters by reference and return owned EZStrings. This provides maximum flexibility to the caller and avoids requiring clone()s everywhere. EZString's own methods, such as trim() here, already do this.

// bad: requires caller to clone() argument
fn foo(s: EZString) -> EZString { s.trim() }
// good
fn bar(s: &EZString) -> EZString { s.trim() }

That being said, sometimes taking by value is unavoidable. In this case, you need to clone your string. Remember, this doesn't actually copy the string, it just increments the reference count.

The simplest and most standard way is to call .clone(). However, if this is too verbose for your taste, there is also a shorthand .c() method. c() also has the advantage of always cloning the underlying EZString, even if you call it on nested references (clone() clones the reference instead in this case).

let mut v: Vec<EZString> = Vec::new();
let s = ez("foo");
let rs = &s;
let rrs = &rs;

// v.push(rrs.clone()); // compile error


Most libraries operate on Strings and &strs, rather than EZStrings. Luckily, EZString Derefs to &str, so in most cases, you can pass &s in and it will just work,

fn take_str(_: &str) {}
let s = ez("");
let rs = &s;


In complicated cases, such as with generic functions, inference may not work. In that case, you can explicitly get a &str via as_str().


If a function requires an owned String, you can use the to_string() method.

fn take_string(_: String) {}

String searching

The contains(), starts_with(), ends_with(), find(), and rfind() methods are generic, meaning that you'll get a confusing compile error if you naively pass in an EZString. The easiest solution is to use as_str() as mentioned in the previous section. Alternatively, you can write &*s for EZStrings and &**s for &EZStrings. No special syntax is required to pass in a literal.

let s = ez("Hello, world!");

assert!(s.contains("o, wo"));
assert_eq!(s.find("ld"), Some(10));
assert_eq!(s.find("l"), Some(2));
assert_eq!(s.rfind("l"), Some(10));

let p = ez("wor");
let r = &p;

Note that find() and rfind() return an Option. To get behavior similar to Python's str.index(), which throws if the substring isn't present, just call unwrap() on the result.

assert_eq!(s.find("ld").unwrap(), 10);

String splitting

You can split by newlines, whitespace, or a provided substring. The returned iterators wrap the results in new EZStrings.

let s = ez(" Hello,   world!\nLine two. ");

assert_eq!(s.lines().collect::<Vec<_>>(), vec![ez(" Hello,   world!"), ez("Line two. ")]);
           vec![ez("Hello,"), ez("world!"), ez("Line"), ez("two.")]);

let s = ez("aaa-bbb-ccc");
assert_eq!(s.split("-").collect::<Vec<_>>(), vec![ez("aaa"), ez("bbb"), ez("ccc")]);
assert_eq!(s.rsplit("-").collect::<Vec<_>>(), vec![ez("ccc"), ez("bbb"), ez("aaa")]);

You can also limit the number of splits via splitn().

let s = ez("aaa-bbb-ccc");
assert_eq!(s.splitn(2, "-").collect::<Vec<_>>(), vec![ez("aaa"), ez("bbb-ccc")]);
assert_eq!(s.rsplitn(2, "-").collect::<Vec<_>>(), vec![ez("ccc"), ez("aaa-bbb")]);

split_terminator() and rsplit_terminator() are the same as split()/rsplit() except that if the final substring is empty, it is skipped. This is useful if the string is terminated, rather than seperated, by a seperator.

let s = ez("aaa-bbb-");
assert_eq!(s.split("-").collect::<Vec<_>>(), vec![ez("aaa"), ez("bbb"),  ez("")]);
assert_eq!(s.split_terminator("-").collect::<Vec<_>>(), vec![ez("aaa"), ez("bbb")]);
assert_eq!(s.rsplit_terminator("-").collect::<Vec<_>>(), vec![ez("bbb"), ez("aaa")]);

let s = ez("aaa-bbb");
assert_eq!(s.split("-").collect::<Vec<_>>(), vec![ez("aaa"), ez("bbb")]);
assert_eq!(s.split_terminator("-").collect::<Vec<_>>(), vec![ez("aaa"), ez("bbb")]);

Although the iterators are lazy, they hold a reference to a copy of the string at time of creation. Therefore, if you later modify the string, the iteration results don't change.

let mut s = ez("aaa-bbb-ccc");
let it = s.split("-");
s += &"-ddd";
assert_eq!(it.collect::<Vec<_>>(), vec![ez("aaa"), ez("bbb"), ez("ccc")]);
let it2 = s.split("-");
assert_eq!(it2.collect::<Vec<_>>(), vec![ez("aaa"), ez("bbb"), ez("ccc"), ez("ddd")]);

Returning Iterators

Every iteration method returns a distinct type. If you want to return one of several iterators, you need to either box them or eagerly evaluate them.

For example, suppose you wanted to emulate Python's str.split() method, which splits on a substring if one is passed in and splits on whitespace if no argument is passed. The naive approach doesn't work as EZString::split() and EZString::split_whitespace() return distinct types. One solution is to eagerly evaluate them and return a list of strings.

fn split<'a, P: Into<Option<&'a str>>>(s: &EZString, sep: P) -> Vec<EZString> {
    match sep.into() {
        Some(sep) => s.split(sep).collect(),
        None => s.split_whitespace().collect(),

let s = ez("x  x-x 77x");
assert_eq!(split(&s, "x"), vec![ez(""), ez("  "), ez("-"), ez(" 77"), ez("")]);
assert_eq!(split(&s, None), vec![ez("x"), ez("x-x"), ez("77x")]);

Alternatively, you can box the iterators, thus preserving the laziness.

fn split<'a, P: Into<Option<&'a str>>>(s: &EZString, sep: P) -> Box<Iterator<Item=EZString>> {
    match sep.into() {
        Some(sep) => Box::new(s.split(sep)),
        None => Box::new(s.split_whitespace()),


The trim(), trim_left(), and trim_right() methods trim whitespace from the ends of the string.

assert_eq!(ez("  hello \n ").trim(), "hello");
let s = ez("  hello \n ").trim_right();
assert_eq!(s, "  hello");
assert_eq!(s.trim_left(), "hello");

trim_left_matches() and trim_right_matches() trim matches of a given substring from the ends of the string. Note that unlike Python, they do not take a set of characters to trim, but a substring. Note that trim_matches() is different from all of the other methods. It takes a char rather than a substring.

assert_eq!(ez("  hello   ").trim_matches(' '), "hello");
let s = ez(" x xhello x x x").trim_right_matches(" x");
assert_eq!(s, " x xhello");
assert_eq!(s.trim_left_matches(" x"), "hello");

String replacement

You can replace one substring with another via .replace().

let s = ez("one fish two fish, old fish, new fish");
assert_eq!(s.replace("fish", "bush"), "one bush two bush, old bush, new bush");
assert_eq!(s.replace(&ez("fish"), &ez("bush")), "one bush two bush, old bush, new bush");

You can also replace the first n occurences of a substring via .replacen()

let s = ez("one fish two fish, old fish, new fish");
assert_eq!(s.replacen("fish", "bush", 3), "one bush two bush, old bush, new fish");
assert_eq!(s.replacen(&ez("fish"), &ez("bush"), 2), "one bush two bush, old fish, new fish");

Other methods

to_lowercase(), to_uppercase(), and repeat() are pretty much self explanatory.

let s = ez("Hello, World!");
assert_eq!(s.to_lowercase(), "hello, world!");
assert_eq!(s.to_uppercase(), "HELLO, WORLD!");
assert_eq!(s.repeat(3), "Hello, World!Hello, World!Hello, World!");

Note that to_lowercase and to_uppercase are Unicode aware, but locale independent. i.e. there is no way to get Turkish capitalization for 'i'.

let s = ez("ὈΔΥΣΣΕΎΣ");
assert_eq!(s.to_lowercase(), "ὀδυσσεύς");

Pointer equality

The == operator tests for value equality, that is whether the given strings contain the same bytes. If you want to test whether two EZStrings share the same underlying buffer, you can use the ptr_eq() method. Note that since EZString is copy-on-write, there is no observeable effect of sharing buffers, apart from reduced memory usage. Therefore, this method is rarely useful.

let a = ez("xxx");
let mut b = a.clone();
let c = &ez("xx") + &ez("x");
assert!(b == c && !b.ptr_eq(&c));

b += &"foo";
// += is copy on write, so b no longer points to a
assert!(a == "xxx");
assert!(b == "xxxfoo");