pub fn prop_get_mandatory_from<'a, I, T>(
    map: &'a PropMap,
    key: &str
) -> Result<T, Box<dyn Error>>where
    T: TryFrom<&'a I, Error = Box<dyn Error>>,
    I: 'static,
Expand description

Like prop_get_optional_from(), but eliminates the inner Option by turning missing keys into errors.