-- --[[
--     lua-rubble: Rust-like struct-trait-impl system
--     https://github.com/evolbug/lua-rubble
-- ]]

-- function struct(members)
--     assert(type(members) == 'table', 'must use table for call')
--     return setmetatable({
--         impls = {},
--         traits = {},
--     }, {
--         __index = {
--             impl = function(self, methods)
--                 assert(type(methods) == 'table', 'must use table for methods')
--                 assert(#methods == 0, 'only named members allowed')
--                 for k, v in pairs(methods) do
--                     assert(type(k) == 'string', 'name must be a string')
--                     assert(type(v) == 'function', 'not a method')
--                     assert(not self.impls[k], 'method ' .. k .. ' already defined')
--                     self.impls[k] = v
--                 end
--             end,
--         },

--         __call = function(self, init)
--             assert(type(init) == 'table', 'must use table for init')
--             assert(#init == 0, 'only named members allowed')
--             for key, value in pairs(init) do
--                 assert(members[key], 'initializing nonexistent field ' .. key)
--                 assert(type(value) == members[key],
--                     "type mismatch for member " .. key .. ' expected:' .. members[key] .. ' got:' .. type(value))
--             end
--             return setmetatable(init, {
--                 __index = self.impls,
--                 __newindex = function(self, key, value)
--                     assert(members[key], "setting nonexistent member " .. key)
--                     assert(type(value) == members[key],
--                         "type mismatch for member " .. key .. ' expected:' .. members[key] .. ' got:' .. type(value))
--                     self[key] = value
--                 end,
--             })
--         end,

--         __newindex = function(self, key, value)
--             error('struct definitions are immutable')
--         end,
--     })
-- end

-- function trait(members)
--     assert(type(members) == 'table', 'must use table for call')
--     return setmetatable(members, {
--         __index = {
--             impl = function(self, struct)
--                 return function(methods)
--                     assert(type(methods) == 'table', 'must use table for methods')
--                     assert(#methods == 0, 'only named members allowed')
--                     for k, v in pairs(self) do
--                         assert(methods[k], 'must implement method ' .. k)
--                         assert(type(methods[k]) == 'function', 'method ' .. k .. ' not a function')
--                     end
--                     for k, v in pairs(methods) do
--                         assert(type(k) == 'string', 'name must be a string')
--                         assert(type(v) == 'function', 'not a method')
--                         assert(self[k], 'method not specified in trait')
--                         assert(not struct.impls[k], 'method ' .. k .. ' already defined')
--                         struct.impls[k] = v
--                     end
--                     struct.traits[self] = true
--                 end
--             end,
--         },
--         __call = function(self, init)
--             assert(type(init) == 'table', 'must use table for init')
--             assert(#init == 0, 'only named members allowed')
--             for k, v in pairs(init) do
--                 assert(members[k], 'initializing nonexistent field')
--             end
--             return setmetatable(init, {
--                 __index = self.impls,
--                 __newindex = function(self, key, value)
--                     assert(members[key], "setting nonexistent member " .. key)
--                     assert(type(value) == members[key], "type mismatch for member")
--                     self[key] = value
--                 end,
--             })
--         end,

--         __newindex = function(self, key, value)
--             error('trait definitions are immutable')
--         end,
--     })
-- end