Macro generalized_fallible_getter

macro_rules! generalized_fallible_getter {
    ($top_level_method_name:ident, $impl_name:ident, [ $( $arg:ident: $arg_type:ty ,)* ],  $ret_type:ty) => { ... };
}

Expands into a getter method that forwards all its arguments and returns a fallible value which is the same as the value returned by the underlying function.

The invocation:

impl _ {
    generalized_fallible_getter!(
        get_context,
        unum_getContext,
        [context_type: sys::UDisplayContextType, ],
        sys::UDisplayContext
    );
}

allows us to bind the function:

UDisplayContext unum_getContext(
    const SOMETYPE* t,
    UDisplayContextType type,
    UErrorCode* status
);

which then becomes:

impl _ {
  fn get_context(&self, context_type: sys::UDisplayContextType) -> Result<sys::UDisplayContext, common::Error>;
}

where Self has an internal representation named exactly Self::rep.