Accessing the last element of a vector

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• Unlike Python and Perl, rust won't let us use a negative index in a vector so we won't be able to access the last element using vector_name[-1]
• We can either use vector_name.len()-1 or
• We can use vector_name.last(), but in this case we get an Option that can be None as well.

• If we access a seemingly arbitrary element that we calculated using vector_name.len()-1 then either we get back a value or Rust will panic if we gave an index too big.
• On the other hand using last we are more protected. In that case we either get a value or None if the vector was empty.

examples/vectors/last-vec-index/src/main.rs

fn main() {
    let planets: Vec<&str> = vec!["Mercury", "Venus", "Earth"];
    println!("{}", planets.len());
    println!("{}", planets[planets.len() - 1]);
    // println!("{}", planets[ 5 ]);  // thread 'main' panicked at 'index out of bounds: the len is 3 but the index is 5'
    println!("{}", planets.last().unwrap());

    let planets: Vec<&str> = vec![];
    //println!("{}", planets[ planets.len()-1 ]);  // thread 'main' panicked at 'attempt to subtract with overflow'
    println!("{:?}", planets.last()); // None
}

3
Earth
Earth
None