68 lines
2.4 KiB
Lua
68 lines
2.4 KiB
Lua
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--[[
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memoize creates a function as a wrapper that caches the last outputs of a function.
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This is useful if you know that the function should return the same output every
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time it is run with the same inputs. The function should only return an output, and
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not have any side effects. These side effects are not cached.
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Without memoize's caching, even though the function ouputs the same values, the
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memory locations of the values are different; tables made in the function, even if
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they have the same values, won't be the same tables.
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memoize only caches the last set of inputs and ouputs. This means that it is only
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helpful when the function is likely to be called with the same inputs multiple
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times in a row. This is the case with most Roact use cases.
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Note that memoize only does a ** shallow check on table inputs ** . This means
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that if the same table is input but the elements of the table are different then
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it will be assumed that the table has not changed.
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In addition to all the previous warnings, memoize strips trailing nils. This means
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that if foo is a memoized function and we call foo(), then foo(nil) will return a
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cached value. This is opposed to how print handles input. print() only outputs a
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new line, but print(nil) outputs "nil". This is because varargs can detect the
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number of arguments passed in. So, be careful when using memoize with varargs.
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Trailing nils will be stripped.
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The wrapper can take any number of inputs and give any number of outputs.
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Leading and interspersed nils are handled gracefully. Trailing nils on the input
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are stripped.
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]]
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local function captureSize(...)
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return {...}, select("#", ...)
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end
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local function memoize(func)
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assert(type(func) == "function", "memoize requires a function to memoize")
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local lastArgs
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local lastNumArgs
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local lastOutput
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local lastNumOutput
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return function(...)
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local numArgs = select("#", ...)
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while numArgs > 0 and select(numArgs, ...) == nil do
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numArgs = numArgs - 1
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end
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if numArgs ~= lastNumArgs then
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lastArgs = {...}
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lastNumArgs = numArgs
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lastOutput, lastNumOutput = captureSize(func(...))
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return unpack(lastOutput, 1, lastNumOutput)
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end
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for i = 1, lastNumArgs do
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if select(i, ...) ~= lastArgs[i] then
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lastArgs = {...}
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lastOutput, lastNumOutput = captureSize(func(...))
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break
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end
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end
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return unpack(lastOutput, 1, lastNumOutput)
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end
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end
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return memoize
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