Function add_argument 

pub fn add_argument<'t, DB, T>(
    values: &mut Vec<Value>,
    value: T,
) -> Result<(), BoxDynError>
where
    DB: Database<ArgumentBuffer = Vec<Value>>,
    T: Encode<'t, DB> + Type<DB>,

Encodes value onto values, as one placeholder’s worth.

What a driver’s Arguments::add does: whatever the encoder does, exactly one value lands for the placeholder, or none if it fails.

Errors

When encoding fails, in which case values is left as it was.