Macro define_row_builder 

macro_rules! define_row_builder {
    (
        struct $name:ident<$lifetime:lifetime $(, $generic:ident $( : $bound:path )? )*>
        $( where $where_path:path: $where_bound:path $(,)? )?
        $({ $( $field:ident: $field_type:ty ),+ $(,)? })?,
        |$array_param:ident| -> $array_type:ty { $init_expr:expr }
        $(, |$value:ident| $(-> Option<$option_ty:ty>)? $value_transform:expr )?
    ) => { ... };
}

Macro to define (possibly generic) row builders with consistent structure and behavior.

The macro optionally allows to define a transform for values read from the underlying array. Transforms of the form |value| { ... } are infallible (and should produce something that implements Into<Variant>), while transforms of the form |value| -> Option<_> { ... } are fallible (and should produce Option<impl Into<Variant>>); a failed tarnsform will either append null to the builder or return an error, depending on cast options.

Also supports optional extra fields that are passed to the constructor and which are available by reference in the value transform. Providing a fallible value transform requires also providing the extra field options: &'a CastOptions.