Module 3Structs & MethodsLesson 2 of 922 min

impl Methods & Associated Functions

Position::new, market_value, and unrealized PnL with &self.

impl blocks

rust

struct Position {
    qty: f64,
    avg_price: f64,
}

impl Position {
    fn new(qty: f64, avg_price: f64) -> Self {
        Self { qty, avg_price }
    }

    fn market_value(&self, mark: f64) -> f64 {
        self.qty * mark
    }
}

fn main() {
    let pos = Position::new(100.0, 50.0);
    println!("MV={:.2}", pos.market_value(53.25));
}

Output

MV=5325.00

Receiver types

Receiver	Meaning
`&self`	read-only method
`&mut self`	may mutate
`self`	consumes the value

Associated vs method

Position::new(...) — no instance yet
pos.market_value(mark) — called on instance

Unrealized PnL

For a simple linear position:

uPnL = qty * (mark - avg_price)

(works for shorts if qty is signed)

Exercise

Challenge

Add is_long/is_flat and test a short position qty=-40, avg=50, mark=48.

Tips

Self in impl means the struct type
&self does not take ownership
Keep formulas in methods for reuse

Try it live

impl Methods & Associated FunctionsRust 2021

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Output

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