Here’s the code, I am trying to run:
use std::vec::Vec;
fn main () {
let percentages = [10, 11, 23, 34];
let balance = compound( 1000.00, percentages);
println!("Your balance is {}", balance );
}
fn compound(investment: f64, returns: Vec<f64> ) -> f64 {
returns.fold(investment, | value, perc | value * ( 1 + (&perc / 100 )) )
}
A detailed explanation on why I am getting the found : [_; 4] would be much appreciated.
Thanks in advance for your time.
You seem to have defined percentages as an array.
[10, 11, 23, 34]
is the syntax for arrays, in this case an array of length 4. Hence the type error.
There is a convenient macro you can use to make a Vec from an array, which looks like this:
vec![a, b, c, ...]
In your case, you’ve actually written integers instead of floating point numbers, so you’d want to initialize percentages like so:
let percentages = vec![10.0, 11.0, 23.0, 34.0];
Thanks for the tips @zsck, I tried them:
use std::vec::Vec;
fn main () {
let percentages = vec![10.0, 11.0, 23.0, 34.0];
let balance = compound( 1000.00, percentages);
println!("Your balance is {}", balance );
}
fn compound(investment: f64, returns: Vec<f64> ) -> f64 {
returns.fold(investment, | value, perc | value * ( 1 + (perc / 100 )) )
}
Now, I am getting the error:
`error: no method named `fold` found for type `std::vec::Vec<f64>` in the current scope`
I am hacking up a trait tonight that implements this type of operation easily (passing integer or float and array[] -> f64) and share it on cargo, hopefully others won’t struggle with edge cases.
Guess I have been spoiled with how JS arrays work 
Use Vec::iter() to get an iterator on which you can use the iterator methods. Also, you need to use floating point values instead of ints.
use std::vec::Vec;
fn main () {
let percentages = vec![10.0, 11.0, 23.0, 34.0];
let balance = compound( 1000.00, percentages);
println!("Your balance is {}", balance );
}
fn compound(investment: f64, returns: Vec<f64> ) -> f64 {
returns.iter().fold(investment, | value, perc | value * ( 1. + (perc / 100. )) )
}
Now that the question of how to pass in Vecs has been answered, another point should be brought up:
If your argument type is a Vec, the ownership of the Vec is passed to the called function and so the Vec is no longer available to the caller. So, if you’d try something like:
let balance = compound( 1000.00, percentages);
let balance = compound( balance, percentages);
it will fail to compile with the error "use of moved value: percentages".
For this reason, a function like compound would usually take the returns Array/Vec as a reference. (i.e. &Vec, with the caller passing it using &percentages).
Now, once you take an immutable reference to a Vec, you can almost always rather take a slice (i.e. &[f64]), so that the caller can pass in data from a Vec OR an array:
fn main () {
let percentages = [10., 11., 23., 34.];
let balance = compound( 1000.00, &percentages);
println!("Your balance is {}", balance );
}
fn compound(investment: f64, returns: &[f64] ) -> f64 {
returns.iter().fold(investment, | value, &perc | value * ( 1. + (perc / 100. )) )
}