在C#中我如何memoize的函数有两个参数?
In C# how do I memoize a function with two arguments?
我必须记忆化之前,咖喱?
Do I have to curry before memoization?
韦斯代尔写了记忆化code 我通常使用,但现在我需要两个参数
Wes Dyer wrote the Memoization code I typically use, but now I need two arguments
您只需要把memoize的方法有三个泛型类型,并采取有两个参数,这两个参数的函数的重载版本。它仍然会返回一个无参数功能:
You just make an overloaded version of the Memoize method that has three generic types and takes a function with two parameters, and the two arguments. It still returns a parameterless function:
public static Func<R> Memoize<A1,A2,R>(this Func<A1,A2,R> f, A1 a1, A2 a2)
{
R value = default(R);
bool hasValue = false;
return () =>
{
if (!hasValue)
{
hasValue = true;
value = f(a1,a2);
}
return value;
};
}
编辑: 另外,你需要创建一个自定义的IEqualityComparer为包含两个参数的KeyValuePair,为memoize的方法能够返回一个函数有两个参数:
Alternatively, you need to make a custom IEqualityComparer for a KeyValuePair that contains the two arguments, for the Memoize method to be able to return a function with two parameters:
public static Func<A1,A2,R> Memoize<A1,A2,R>(this Func<A1,A2,R> f, IEqualityComparer<KeyValuePair<A1,A2>> comparer)
{
var map = new Dictionary<KeyValuePair<A1,A2>,R>(comparer);
return (a1,a2) =>
{
R value;
KeyValuePair<A1,A2> key = new KeyValuePair<A1,A2>(a1,a2);
if (map.TryGetValue(key, out value)) {
return value;
}
value = f(a1,a2);
map.Add(key, value);
return value;
};
}