如何编写通用的记忆功能? [英] How do I write a generic memoize function?

问题描述

我正在编写一个函数来查找三角形数和自然的写法是递归的:

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

但尝试计算前 100,000 个三角形数失败，一段时间后堆栈溢出.这是 memoize 的理想函数，但我想要一个解决方案，可以记住我传递给它的任何函数.

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

我敢打赌这样的事情应该适用于 Lua 中的可变参数列表:

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

您可能还可以使用带有 __tostring 的元表做一些聪明的事情，以便可以使用 tostring() 转换参数列表.哦，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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