Can't create IcmpSocketBuffer without heap allocation

[steynh]

I would like to create an IcmpSocket without the use of heap, like this:

let icmp_socket = {
    static mut ICMP_RX_DATA: [u8; 256] = [0; 256];
    static mut ICMP_TX_DATA: [u8; 256] = [0; 256];
    static mut ICMP_RX_METADATA: [PacketMetadata<smoltcp::wire::IpAddress>;1] = [IcmpPacketMetadata::empty(); 1];
    static mut ICMP_TX_METADATA: [PacketMetadata<smoltcp::wire::IpAddress>;1] = [IcmpPacketMetadata::empty(); 1];

    let icmp_rx_buffer = IcmpSocketBuffer::new(unsafe { &mut ICMP_RX_METADATA[..] }, unsafe { &mut ICMP_RX_DATA[..] });
    let icmp_tx_buffer = IcmpSocketBuffer::new(unsafe { &mut ICMP_TX_METADATA[..] }, unsafe { &mut ICMP_TX_DATA[..] });

    IcmpSocket::new(icmp_rx_buffer, icmp_tx_buffer)
};

However, I can't seem to make a PacketMetadata buffer without using heap allocation. Because PacketMetadata::empty() is not const, it's not possible to use it during static initialization.

Is there another way to accomplish this?