It is a special-purpose performance improvement feature and is not recommended for general use.
它是一个特殊用途的性能改进特性，不建议普遍使用。
2
Just as an MC is a special-purpose object, its definition is a special-purpose class which defines the structure and behavior of its instances.
正如MC是专用对象一样，其定义也是专用类，用于定义其实例的结构和行为。
3
You will remember that the Bank of England once issued two notes of a million pounds each, to be used for a specialpurpose connected with some public transaction with a foreign country.