@@ -17,10 +17,22 @@ local create_table = function(...) return { ... } end +local make_generator_mt = function(fn) + return + { + __index = function(t, k) + local v = fn(k) + t[k] = v + return v + end; + } +end + return { do_nothing = do_nothing; identity = identity; invariant = invariant; create_table = create_table; + make_generator_mt = make_generator_mt; } lua-nucleo/functional.lua @@ -20,13 +20,15 @@ local do_nothing, identity, invariant, create_table, + make_generator_mt, functional_exports = import 'lua-nucleo/functional.lua' { 'do_nothing', 'identity', 'invariant', - 'create_table' + 'create_table', + 'make_generator_mt' } -------------------------------------------------------------------------------- @@ -133,4 +135,59 @@ end) -------------------------------------------------------------------------------- +test:tests_for "make_generator_mt" + +-------------------------------------------------------------------------------- + +test "make_generator_mt-nil" (function() + local num_calls = 0 + + local mt = make_generator_mt( + function(k) + num_calls = num_calls + 1 + return nil + end + ) + + local t = setmetatable({ }, mt) + + ensure_equals("no calls", num_calls, 0) + ensure_equals("get 42", t[42], nil) + ensure_equals("one call", num_calls, 1) + ensure_equals("get A", t["A"], nil) + ensure_equals("two calls", num_calls, 2) + ensure_equals("get 42 again", t[42], nil) + ensure_equals("nill not cached", num_calls, 3) +end) + +test "make_generator_mt-echo" (function() + local num_calls = 0 + + local mt = make_generator_mt( + function(k) + num_calls = num_calls + 1 + return k + end + ) + + local t = setmetatable({ ["A"] = "B" }, mt) + + ensure_equals("no calls", num_calls, 0) + ensure_equals("get 42", t[42], 42) + ensure_equals("one call", num_calls, 1) + ensure_equals("get 42 again", t[42], 42) + ensure_equals("value cached", num_calls, 1) + + ensure_equals("predefined value", t["A"], "B") + ensure_equals("still one call", num_calls, 1) + + local k = {} + ensure_equals("get {}", t[k], k) + ensure_equals("two calls", num_calls, 2) + ensure_equals("get {} again", t[k], k) + ensure_equals("still two calls", num_calls, 2) +end) + +-------------------------------------------------------------------------------- + assert(test:run()) test/functional.lua 0d47551da2c7e3a27154e66b184eccb6e891e7be Alexander Gladysh agladysh@gmail.com http://github.com/lua-nucleo/lua-nucleo/commit/6d26f477280fac445a296c820c2d3d81d439567f 6d26f477280fac445a296c820c2d3d81d439567f 2009-11-14T16:39:11-08:00 2009-11-14T16:39:11-08:00 functional: make_generator_mt bf2e5ae3ab4fbdf1c78a46eb455f457a42ef6553 Alexander Gladysh agladysh@gmail.com