Why is Rust faster than Nim in this CSV parsing example?

[matkuki]

Could someone please make the OP's example:
    
    
    # Code used to parse CSV file
    import std/strutils
    import std/sequtils
    
    let csv = readFile("./nim.csv")
    
    proc sum(s: seq[int]): int = s.foldl(a + b)
    
    var totalSum = 0
    
    for l in csv.splitLines():
        if l.len > 1:
            let rowSum = l.split(",").mapIt(it.parseInt).sum()
            totalSum += rowSum
    
    echo "Expected total = ", 2999999 * 3000000 / 2
    echo "Actual total = ", totalSum
    
    
    Run

... in the `View types / lent / COW strings / ...` magic way everyone has 
started talking about?

I for one don't know what exactly you are discussing and would be genuinely 
greatful if someone could provide an example, thanks.