E0127

Only a name here

Error

Built from the repository at commit a8614dc.

A pattern at a class, array or f64 position takes only a name, which binds the value, or _, which ignores it. Variants are not patterns there.

Why

These types have no variants to tell apart. Bind the value and read its fields or test it inside the arm.

Broken

class Point {
    x: i64
}

enum Slot {
    Full(Point)
}

fn main() {
    let s = Slot.Full(Point(x: 1))
    let n = match s {
        Full(Point(x)) => x
    }
    print(n)
}

What sisu says

error[E0127]: a `Point` position takes only a name or `_`
  --> E0127.sisu:12:14
   |
12 |         Full(Point(x)) => x
   |              ^^^^^^^^

sisu: 1 error
sisu: for more on a code, run `sisu explain <code>`: E0127

Fixed

class Point {
    x: i64
}

enum Slot {
    Full(Point)
}

fn main() {
    let s = Slot.Full(Point(x: 1))
    let n = match s {
        Full(p) => p.x
    }
    print(n)
}