Introduce macro for ThingListBuilder, and use for AuthorityListBuilder

Ian Jacksonrequested to merge
Diziet/arti:config-sub-list into main

This is the first part of #447 (closed) which is part of #371 (closed) which is part of #285 (closed)

Edited by Ian Jackson

Merge request reports

crates/tor-basic-utils/src/lib.rs

+30 −0
Changes for crates/tor-basic-utils/src/lib.rs: 30 added lines, 0 removed lines.
Original line number Original line Diff line number Diff line
@@ -140,3 +140,33 @@ macro_rules! define_accessor_trait { 
}

}





// ----------------------------------------------------------------------

// ----------------------------------------------------------------------



/// Helper for assisting with macro "argument" defaulting

///

/// ```ignore

/// macro_coalesce_args!{ [ something ]  ... }  // =>   something

/// macro_coalesce_args!{ [ ], [ other ] ... }  // =>   other

/// // etc.

/// ```

///

/// ### Usage note

///

/// It is generally possible to avoid use of `macro_coalesce_args`, at the cost of

/// providing many alternative matcher patterns.  Using `macro_coalesce_args` can make

/// it possible to provide a single pattern with the optional items in `$( )?`.

///

/// This is valuable because a single pattern with some optional items

/// makes much better documentation than several patterns which the reader must compare

/// by eye - and it also simplifies the implementation.

///

/// `macro_coalesce_args` takes each of its possible expansions in `[ ]` and returns

/// the first nonempty one.

#[macro_export]

macro_rules! macro_coalesce_args {

    { [ $($yes:tt)+ ] $($rhs:tt)* } => { $($yes)* };

    { [ ]$(,)? [ $($otherwise:tt)* ] $($rhs:tt)* } => {

        $crate::macro_coalesce_args!{ [ $($otherwise)* ] $($rhs)* }

    };

}



// ----------------------------------------------------------------------