CODEWITHSUNDEEP
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pengowen123
pengowen123

Reputation: 1017

How to make a compile time error if an enum variant is passed to a function

Suppose I have an enum:

enum Foobar {
    Foo(i32),
    Bar(f64)
}

I also have a function that takes a Foobar as an argument:

fn foo(x: &mut Foobar) {
    match x {
        Foobar::Foo(i32) => { /* do something */ },
        Foobar::Bar(f64) => { /* panic */ }
    }
}

Is it possible to throw a compile time error if the caller of the function passes the Bar variant to the function, without using a compiler plugin?

Upvotes: 3

Views: 956

Answers (1)

DK.
DK.

Reputation: 58975

No.

Even a compiler plugin (by which I assume you mean a "lint") can't possibly cover all cases.

If you want to make it statically impossible to pass a particular piece of data to the function, then change the types so that it's actually not valid: define a sibling of Foobar that doesn't have the Bar variant, along with some conversions between the two.

There is no simple or automatic way to do this in Rust; you'll just have to do the hard yakka. Or wait for refinement types, but I wouldn't recommend doing that.

Upvotes: 4

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