Macro enum_field_use 

macro_rules! enum_field_use {
    (mut $self:expr, $a:ident) => { ... };
    (mut $self:expr, $a:ident _ $b:ident) => { ... };
    (mut $self:expr, $a:ident _ $b:ident _ $c:ident) => { ... };
    ($self:expr, $a:ident) => { ... };
    ($self:expr, $a:ident _ $b:ident) => { ... };
    ($self:expr, $a:ident _ $b:ident _ $c:ident) => { ... };
}

Combines one or more unit-enum idents to form a snake_case field name.