The basic idea of iterators is to start with something that you can get an iterator on; an array or a slice is what we have discussed. Then, get the iterator. Finally, find an iterator function that is useful to you. Many iterator functions do not require you to do much. For example:
fn main() {
let v = vec![1,2,3,4,5,6,7,8,9];
let sm :i32 = v.iter().sum();
println!("{:?} sums to {}", v, sm);
}
Other iterator functions require you to provide an anonymous function to do work. For example:
fn main() {
let v = vec![1,2,3,4,5,6,7,8,9];
let sm :i32 = v.iter().fold(0, |acc, e| acc+e );
println!("{:?} sums to {}", v, sm);
let sm :i32 = v.iter().fold(0, |acc, e| acc+e*e );
println!("{:?} sum of squares to {}", v, sm);
}
the fold starts with a value (0 in the examples) and passes that value into the provided anonymous function as the first parameter with the second parameter coming from the iterator. The int passes the result of the function as the value in the next iteration. So the first use of fold does exactly a sum of the items in the vector.
The iterator functions are well documented at https://doc.rust-lang.org/std/iter/trait.Iterator.html
In some cases, iterator functions themselves return iterators. In this case, you can use the "collect()" function to turn the iterator into something more usable, like a vector. For example, the following example starts with a vector of integers and results in a vector of integers in which each element of the original list is cubed.
fn main() {
let v = vec![1,2,3,4,5,6,7,8,9];
let vvv:Vec = v.iter().map(|e| e*e*e).collect();
println!("{:?} transforms to {:?}", v, vvv);
}
Frequently you can do fairly complex operations by passing the results of one iterator function to another iterator function. In this lab/assignment you will not do anything terribly complex, just do some fairly straightforward things with iterators.
This document is the basis of BOTH lab 9 and Homework 5. The basic idea is that you do the first two "problems" as lab 9 and the last 4 as homework 5.
let v = vec!["Aa", "SS", "dd", "FF", "Geoff"];
Do this in 2 steps. First transform the string literals into Strings, then lower case the String. (Yes I know you can do this in one step). (Hint, use map.)
aa bb cc abcde cc
then the result should be 80.
aa bb cc abcde cc
the result should be
aa 2
bb 2
cc 2
abcde 5
cc 2
Hint use for_each
1a a2 33 66t ttt
then you should end up with only
1a 33 66t
let v :Vec = String::from("we the people of the united states").chars().collect();
Note that the "chars" function returns an iterator from an owned string.
Now use an iterator function to put all of these characters back into a string, AFTER shifting each character by +1. Finally, print the resulting string.
If you used my string, your printout should be:
xf!uif!qfpqmf!pg!uif!vojufe!tubuft
Finally, put your encoder into a function that takes a string and a number and returns a string. In a main function, pass a string from the command line and +1. Print that string. Then pass the returned string back to the function with -1. Print the decoded string. You should get back your original string.
for i in 0..10 {
println("{}", i);
}
Explain how your program demonstrates that iterators are actually lazy.
Put everything you want to submit in a directory containing nothing else. For instance you might name the directory a4