main.rs

#[derive(PartialEq)]
struct ConfigData {
    id: u32,
    enabled: bool,
    params: (f32, f32), // Nested tuple
}

#[derive(PartialEq)]
enum ComplexEnum<'a> {
    SimpleVariant,                      // No data
    Count(i64),                         // Single primitive data
    Coords((i32, i32, i32)),            // Tuple data
    UserData { name: &'a str, age: u8 }, // Struct-like variant
    RawData([u8; 8]),                   // Array data
    Settings(ConfigData),               // Struct data
}

fn main() {
    // Initialize with one variant
    let mut current_state = ComplexEnum::UserData {
        name: "Alice",
        age: 30,
    };

   // Access initial values using match
    match current_state {
        ComplexEnum::UserData { ref name, age } => {
            assert!(*name == "Alice", "Initial name should be Alice");
            assert!(age == 30, "Initial age should be 30");
        }
        _ => panic!("Initial state should be UserData!"),
    } 

    // Access initial values using if let
    if let ComplexEnum::UserData { name, .. } = current_state {
        assert!(name.starts_with('A'), "Name should start with A");
    } else {
        panic!("Still expect UserData here!");
    } 

    // Mutate the enum variable to a different variant (Settings)
    current_state = ComplexEnum::Settings(ConfigData {
        id: 123,
        enabled: true,
        params: (1.0, -0.5),
    });

    // Access nested values in the new variant
     match current_state {
        ComplexEnum::Settings(config) => {
            assert!(config.id == 123, "Settings ID should be 123");
            assert!(config.enabled, "Settings should be enabled");
            assert!(config.params.0 == 1.0, "Settings params.0 should be 1.0");
            assert!(config.params.1 == -0.5, "Settings params.1 should be -0.5");
        }
        _ => panic!("State should now be Settings!"),
    } 

    // Mutate the enum variable to a different variant (RawData)
    current_state = ComplexEnum::RawData([0, 1, 2, 3, 4, 5, 6, 7]);

    // Mutate data *inside* the RawData variant
    let mut mutated_internally = false;
    match &mut current_state {
        // Use mutable borrow (&mut) to modify internal data
        ComplexEnum::RawData(data_array) => {
            assert!(data_array[0] == 0, "RawData[0] should be 0 initially");
            assert!(data_array[7] == 7, "RawData[7] should be 7 initially");

            // Modify elements
            data_array[0] = 100;
            data_array[7] = 200;
            data_array[1] *= 5; // Modify based on existing value

            mutated_internally = true;
        }
        _ => {  /*No mutation needed for other branches in this step*/  }
    }
    assert!(mutated_internally, "Internal mutation should have happened"); 

    // Assert internal mutations in RawData
     if let ComplexEnum::RawData(data_array) = current_state {
        assert!(data_array[0] == 100, "RawData[0] should now be 100");
        assert!(data_array[1] == 5, "RawData[1] should now be 5 (1*5)");
        assert!(data_array[7] == 200, "RawData[7] should now be 200");
    } else {
        panic!("State should still be RawData after internal mutation!");
    } 

    // Mutate data *inside* the nested ConfigData struct within Settings variant
   current_state = ComplexEnum::Settings(ConfigData {
        // Reset state
        id: 999,
        enabled: false,
        params: (0.0, 0.0),
    });

    match &mut current_state {
        ComplexEnum::Settings(config) => {
            config.enabled = true; // Mutate bool field
            config.params.1 = config.params.0 + 10.0; // Mutate tuple field
            config.id += 1; // Mutate id field
        }
        _ => panic!("State should be Settings for nested mutation!"),
    }

    // Assert internal nested mutations
    match current_state {
        ComplexEnum::Settings(config) => {
            assert!(config.id == 1000, "ConfigData id should be 1000");
            assert!(config.enabled, "ConfigData enabled should be true");
            assert!(
                config.params.0 == 0.0,
                "ConfigData params.0 should be unchanged"
            );
            assert!(config.params.1 == 10.0, "ConfigData params.1 should be 10.0");
        }
        _ => panic!("State should still be Settings after nested mutation!"),
    }

    // Test remaining variants
    current_state = ComplexEnum::Count(5000);
    assert!(current_state == ComplexEnum::Count(5000));
    if let ComplexEnum::Count(c) = current_state {
        assert!(c == 5000);
    } else {
        panic!("State should be Count");
    }

    current_state = ComplexEnum::Coords((-10, 0, 20));
    assert!(current_state == ComplexEnum::Coords((-10, 0, 20)));
    if let ComplexEnum::Coords((x, y, z)) = current_state {
        assert!(x == -10);
        assert!(y == 0);
        assert!(z == 20);
    } else {
        panic!("State should be Coords");
    }

    current_state = ComplexEnum::SimpleVariant;
    assert!(current_state == ComplexEnum::SimpleVariant);
}