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| function defmulti(keyfn) | |
| if not keyfn then | |
| keyfn = function(...) return ... end | |
| end | |
| local multi = { | |
| _keyfn = keyfn, | |
| _methods = {} | |
| } | |
| setmetatable(multi, { | |
| __call = function(self, ...) | |
| local key = self._keyfn(...) | |
| if self._methods[key] then | |
| return self._methods[key](...) | |
| else | |
| if self._methods.default then | |
| return self._methods.default(...) | |
| else | |
| error("no dispatch for key: " .. tostring(key)) | |
| end | |
| end | |
| end | |
| }) | |
| return multi | |
| end | |
| function defmethod(multi, key, fn) | |
| if not multi._methods then | |
| multi._methods = {} | |
| end | |
| multi._methods[key] = fn | |
| end | |
| fib = defmulti(tonumber) | |
| defmethod(fib, 0, function() return 0 end) | |
| defmethod(fib, 1, function() return 1 end) | |
| defmethod(fib, "default", function(n) return fib(n-1) + fib(n-2) end) | |
| print(fib(10)) | |
| greet = defmulti(function(user) return user.name end) | |
| defmethod(greet, "mk", function() return "MK is 1337" end) | |
| defmethod(greet, "mark", function() return "Mark is a lamer" end) | |
| defmethod(greet, "default", function(user) return string.format("%s seems like a nice fellow", user.name) end) | |
| print(greet({name = "mk"})) | |
| print(greet({name = "mark"})) | |
| print(greet({name = "steven"})) |
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