return function (searcher, source)
local stype = source.type
if stype == 'getfield'
or stype == 'setfield' then
return source.field
elseif stype == 'getmethod'
or stype == 'setmethod' then
return source.method
elseif stype == 'getindex'
or stype == 'setindex' then
return source.index
end
return nil
end