How do you make a range in Rust?

Question

The docs don't say how, and the tutorial completely ignores for loops.

Answer 1

As of 1.0, for loops work with values of types with the Iterator trait.

The book describes this technique in chapter 3.5 and chapter 13.2.

If you are interested in how for loops operate, see the described syntactic sugar here:

http://doc.rust-lang.org/std/iter/index.html

Example:

fn main() {
    let strs = ["red", "green", "blue"];

    for sptr in strs.iter() {
        println!("{}", sptr);
    }
}

(Playground)

If you just want to iterate over a range of numbers, as in C's for loops, you can create a numeric range with the a..b syntax:

for i in 0..3 {
    println!("{}", i);
}

If you need both, the index and the element from an array, the idiomatic way to get that is with the Iterator::enumerate method:

fn main() {
    let strs = ["red", "green", "blue"];

    for (i, s) in strs.iter().enumerate() {
        println!("String #{} is {}", i, s);
    }
}

Notes:

• The loop items are borrowed references to the iteratee elements. In this case, the elements of strs have type &'static str - they are borrowed pointers to static strings. This means sptr has type &&'static str so we dereference it as *sptr. An alternative form which I prefer is:

  for &s in strs.iter() {
      println!("{}", s);
  }
  

Answer 2

Actually, the Loops section of the tutorial does cover for loops:

When iterating over a vector, use for instead.

for elt in ["red", "green", "blue"] {
   std::io::println(elt);
}

But if you needed indices, you could do something like the following, using the uint::range function from the core library (or int::range or u8::range or u32::range or u64::range) and Rust's syntax for blocks:

range(0u, 64u, {|i| C[i] = A[i] + B[i]});

Rust used to support this equivalent syntax but it was later removed:

range(0u, 64u) {|i|
    C[i] = A[i] + B[i];
}

Answer 3

for i in range(0, 100) is now deprecated in favour of for i in 0..100 (according to rustc 1.0.0-nightly.

Also worth noting, the compiler can't disambiguate when you use an identifier in the range (e.g. for i in 0..a) so you have to use for i in (0..a), but there's a pull request submitted to fix this.

Answer 4

Note that as of rustc 0.4 (Oct 2012), the alternate construction of

range(0u, 64u) {|i|
    C[i] = A[i] + B[i];
}

appears to not be supported any more.

Answer 5

Use int::range.