Module 3Enums & matchLesson 4 of 922 min

Enums with Data

Side and OrderType — replace stringly-typed trading code.

Enums are alternatives

rust

enum Side { Buy, Sell }

enum OrderType {
    Market,
    Limit(f64),
    Stop { trigger: f64, limit: f64 },
}

Exhaustive match

rust

enum Side { Buy, Sell }

fn label(side: Side) -> &'static str {
    match side {
        Side::Buy => "BUY",
        Side::Sell => "SELL",
    }
}

fn main() {
    println!("{}", label(Side::Buy));
    println!("{}", label(Side::Sell));
}

Output

BUY
SELL

If you add a variant later, the compiler shows every match you forgot — pure gold for production trading code.

Stringly vs typed

Approach	Risk
`side: &str`	"byu" typos
`side: Side`	typos are compile errors

Exercise

Challenge

Add TimeInForce { Day, Gtc, Ioc } and extend describe.

Tips

match must cover every variant
Enums can carry data per variant
Prefer enums over booleans for multi-state logic

Try it live

Enums with DataRust 2021

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Output

Press Run to compile and execute.