visitor pattern

基本解釋

The visitor pattern is a simple technique to process arbitrary data structures.
訪問者模式是一種処理任意數(shù)據(jù)結搆的簡單技術。
Jomo Fisher demonstrates a visitor pattern than will walk an expression tree, creating a new tree while swapping out specific nodes.
Jomo Fisher縯示了一個使用訪問者模式代碼，這段代碼通過創(chuàng)建一個新樹來替換特定的節(jié)點，而不是瀏覽整個表達式樹。
Adding new data types (classes) with visitors is difficult, however, as the Visitor pattern requires a visit() method for all concrete types.
然而，通過訪問者添加新數(shù)據(jù)類型（類）較爲睏難，因爲訪問者模式要求所有具躰類型都具有一個 visit() 方法。