How do you make a range in Rust?
Solution 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 in Module std::iter.
Example:
fn main() {
let strs = ["red", "green", "blue"];
for sptr in strs.iter() {
println!("{}", sptr);
}
}
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 meanssptr
has type&&'static str
, so we dereference it as*sptr
. An alternative form which I prefer is:for &s in strs.iter() { println!("{}", s); }
Solution 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];
}
Solution 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 is 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.
Comments
-
mcandre over 2 years
The documentation doesn't say how and the tutorial completely ignores for loops.
-
mcandre over 12 yearsThanks! I'm curious why Rust has two different syntaxes for function definitions and blocks. Seems like they could save the coder trouble by reusing
fn(args...)
instead of|args|
. -
B. Striegel over 12 years@mcandre Actually, the Ruby-style block syntax
{|args| body}
is used to denote a closure rather than just a function. It's also really convenient for simplifying usage of anonymous functions as you might see them used in Javascript, since any function that accepts a closure as its last argument (such as a callback) can be written after the function call, as in Lindsey's third example above. Finally, even though Rust has a few different types of closures, Rust can infer the type of closure you want when using the block syntax. See also doc.rust-lang.org/doc/tutorial.html#closures -
Warren P about 11 yearsDoes this still work? I can't get range(n,n) {|i| ...} to compile. I get weird errors.
-
Admin almost 11 yearsAs of rust 0.6, for int::range() |i| { C[i] = A[i] + B[i]; } should work. for is syntactic sugar which passes the closure in as an argument, iirc.
-
oli_obk over 9 yearsidentifier ambiguity has been fixed in github.com/rust-lang/rust/pull/21374
-
Amol over 8 yearsif there was an int type, it has been deprecated now.
-
hellow about 5 yearsHe's right. It has been removed so this answer is obsolete.
-
Evgeni Nabokov almost 4 yearsHow to make rev for 0..3?
-
Laurits L. L. almost 4 years@EvgeniNabokov Add parenthesis:
for i in (0..3).rev() { // Code here... }
Reference: doc.rust-lang.org/book/ch03-05-control-flow.html -
wheeler over 3 yearsHow do I make
i
au8
? I didfor i: u8 in 0..26 {
and it is not working. -
zombiesauce over 2 yearsWhy is this not the top answer, despite being the most voted and the accepted answer? SO works in weird ways..