You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lib.rs
    path of file: ./repos/vector/lib/vector-buffers/src
    
    the code of the file until where you have to start completion: //! The Vector Core buffer
//!
//! This library implements a channel like functionality, one variant which is
//! solely in-memory and the other that is on-disk. Both variants are bounded.

#![deny(warnings)]
#![deny(clippy::all)]
#![deny(clippy::pedantic)]
#![allow(clippy::module_name_repetitions)]
#![allow(clippy::type_complexity)] 
    
    fn arbitrary(g: &mut Gen) -> Self {
        // TODO: We explicitly avoid generating "overflow" as a possible value because nothing yet
        // supports handling it, and will be defaulted to to using "block" if they encounter
        // "overflow".  Thus, there's no reason to emit it here... yet.
        if bool::arbitrary(g) {
            WhenFull::Block
        } else {
            WhenFull::DropNewest
        }
    }