如何写一个通用memoize函数？ [英] How do I write a generic memoize function?

问题描述

我在写一个函数来查找三角形数字和自然写的方式是递归的：

I'm writing a function to find triangle numbers and the natural way to write it is recursively:

function triangle (x)
   if x == 0 then return 0 end
   return x+triangle(x-1)
end

计算第一个100,000个三角形数字失败，堆栈溢出一段时间。这是记事的理想功能，但我想要一个解决方案，记住我传递的任何函数

But attempting to calculate the first 100,000 triangle numbers fails with a stack overflow after a while. This is an ideal function to memoize, but I want a solution that will memoize any function I pass to it.

推荐答案

我打赌这样应该适用于Lua中的变量参数列表：

I bet something like this should work with variable argument lists in Lua:

local function varg_tostring(...)
    local s = select(1, ...)
    for n = 2, select('#', ...) do
        s = s..","..select(n,...)
    end
    return s
end

local function memoize(f)
    local cache = {}
    return function (...)
        local al = varg_tostring(...)
        if cache[al] then
            return cache[al]
        else
            local y = f(...)
            cache[al] = y
            return y
        end
    end
end

你也可以用一个metatables __tostring，以便可以使用tostring（）转换参数列表。哦的可能性。

You could probably also do something clever with a metatables with __tostring so that the argument list could just be converted with a tostring(). Oh the possibilities.

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