Rust field `dummy` of struct is private

[lucaszanella]

I'm trying to create a struct like this:

DeviceCapabilities {
    max_transmission_unit: self.mtu,
    ..DeviceCapabilities::default()
}

Here's the struct definition:

#[derive(Debug, Clone, Default)]
pub struct DeviceCapabilities {
    pub max_transmission_unit: usize,

    pub max_burst_size: Option<usize>,

    pub checksum: ChecksumCapabilities,

    /// Only present to prevent people from trying to initialize every field of DeviceLimits,
    /// which would not let us add new fields in the future.
    dummy: ()
}

on the line DeviceCapabilities::default() of ..DeviceCapabilities::default() I get the following error:

field `dummy` of struct `smoltcp::phy::DeviceCapabilities` is private

First of all, why the field dummy is being filled, if the second one is max_burst_size?

Actually the piece of code that instantiates the struct is from a library. There it works but in my library it does not. I understand that field dummy is private as it has no pub, but why it works in the other library?

Also what the .. means? Maybe important to understand what's happening

[alice]

If it works in your other library, then that library can probably access the private field from where it was called. The .. means the following:

let def = DeviceCapabilities::default();
DeviceCapabilities {
    max_transmission_unit: self.mtu,
    max_burst_size: def.max_burst_size,
    checksum: def.checksum,
    dummy: def.dummy,
}