{

// Note: replace only informs the cache which elements

// it would like to remove!

// it does not remove them on its own!

std::size_t curSize = _keyIndex.size();

if (curSize < _size)

{

return;

}

std::size_t diff = curSize - _size;

Iterator it = --_keys.end(); //--keys can never be invoked on an empty list due to the minSize==1 requirement of LRU

std::size_t i = 0;

while (i++ < diff)

{

elemsToRemove.insert(*it);

if (it != _keys.begin())

{

--it;

}

}

}

LRUStrategy的replace操作是，只在curSize超过设定的访问上限_size时触发，把list容器中排在末尾的(curSize-_size)个元素标志为失效。

3. 开销

Poco中的Cache类比std::map要慢，其中开销最大的操作为add操作。采用Time Expire策略的Cache要比采用LRU策略的Cache更慢。并且由于Cache类引入了SharePtr和Strategy，其空间花费也要大于std::map。所以在没有必要使用Cache的情况下，还是使用map较好。

4. 例子

下面是Cache的一个示例：

[cpp]

#include "Poco/LRUCache.h"

int main()

{

Poco::LRUCache myCache(3);

myCache.add(1, "Lousy"); // |-1-| -> first elem is the most popular one

Poco::SharedPtr ptrElem = myCache.get(1); // |-1-|

myCache.add(2, "Morning"); // |-2-1-|

myCache.add(3, "USA"); // |-3-2-1-|

// now get rid of the most unpopular entry: "Lousy"

myCache.add(4, "Good"); // |-4-3-2-|

poco_assert (*ptrElem == "Lousy"); // content of ptrElem is still valid

ptrElem = myCache.get(2); // |-2-4-3-|

// replace the morning entry with evening

myCache.add(2, "Evening"); // 2 Events: Remove followed by Add

}