CODEWITHSUNDEEP
structenumsrust
andrey
andrey

Reputation: 1585

Accessing a struct inside an enum

How do I access field c inside struct of type B_ inside enum of type A in this case?

enum A {
    B(B_),
    D(D_)
}

enum D_ { D_1, D_2 }

struct B_ {
    c: Vec<i32>,
}

Obvious stuff like this doesn't work:

let y = A::B;
y.c = Vec::new();

Upvotes: 2

Views: 1240

Answers (1)

eulerdisk
eulerdisk

Reputation: 4709

I think the first problem is that what you really want is y to be of type A, so it cannot have a field named c in the first place. y can be A::B or A::D. Only if y is an A::B variant, then you can get the B_ object inside the variant and then get the c.

The second problem in your code is that you are not initializing y to be an A::B variant. The expression A::B is of type fn(B_) -> A {A::B} which is a kind of constructor function (automagically generated by the compiler) for A enums.

The following code initialize y correctly and get c:

enum A {
    B(B_),
    D(D_)
}

enum D_ { D_1, D_2 }

struct B_ {
    c: Vec<i32>,
}

fn main() {
    let y = A::B( B_ { c : Vec::new() });

    // Check if y is an A::B, so we can get the B_ object inside
    // by deconstruction. Then we can get c.
    if let A::B(b_) = y {
        println!("{:?}", b_.c);
    }
}

Maybe you thought that A::B is a kind of B type defined "inside" A, which is not how enums work is Rust.

Upvotes: 3

Related Questions