Calculator code in the calculator library crate.

lib.rs

// Full tutorial https://www.youtube.com/watch?v=LJppDNH2CHI 

pub struct Calculator {
    result: f64,
}

impl Calculator {
    /// Creates a new Calculator instance with the initial result set to 0.0.
    pub fn new() -> Self {
        return Self { result: 0.0 };
    }

    /// Adds the values in the provided vector to the calculator's result.
    /// Returns a mutable reference to the Calculator instance for method chaining.
    pub fn add(&mut self, values: Vec<f64>) -> &mut Self {
        for val in values {
            self.result += val;
        }
        return self;
    }

    /// Subtracts the values in the provided vector from the calculator's result.
    /// Returns a mutable reference to the Calculator instance for method chaining.
    pub fn subtract(&mut self, values: Vec<f64>) -> &mut Self {
        for val in values {
            self.result -= val;
        }
        return self;
    }

    /// Returns the current result of the calculator.
    pub fn get_result(&self) -> f64 {
        return self.result;
    }

    /// Sets the result of the calculator to the specified value.
    pub fn set_result(&mut self, result: f64) {
        self.result = result;
    }
}

#[cfg(test)]
mod test {
    use crate::Calculator;

    #[test]
    fn test_addition() {
        let mut calculator = Calculator::new();
        calculator.set_result(4.0);
        calculator.add([5.0, 5.0].to_vec());
        assert_eq!(14.0, calculator.get_result())
    }
}