Conditional skip option

[carsonfarmer]

Hi I'm just wondering if it is possible to provide a conditional skip option, similar to how length is able to use values from previous fields. For example, say I have the following struct:

#[derive(PartialEq, Debug, Readable, Writable)]
struct Page {
    flag: bool,
    #[speedy(skip=flag)]
    conditional: u32
}

In this case, both read and write would "skip" the conditional field if the flag were set to false, and both would include them if set to true.

Is there perhaps a different way to achieve the same result? In my case, I am dealing with an existing encoding format, so I am trying to find ways to get speedy to work in this case.