alias与alias this无关.
Stack!(Point!double) randomPoints(size_t count) {
auto points = new Stack!(Point!double);
// ...
}
可这样:
长名,难读,没必要每个地点都详细说明.如果改,也麻烦,到处改.
alias Points = Stack!(Point!double);
// ...
Points randomPoints(size_t count) {
auto points = new Points;
// ...
}
//还可以更进一步
alias PrecisePoint = Point!double;
alias Points = Stack!PrecisePoint;
语法如下:alias new_name = existing_name;
还有 消歧时很有用.为了更可读:
alias CustomerNumber = int;
alias CompanyName = string;
// ...
struct Customer {
CustomerNumber number;
CompanyName company;
// ...
}
//--------
class Box {
private:
Weight weight_;
public:
alias Weight=double;//别名,以后更改类型也方便
Weight weight() const @property {
return weight_;
}//
// ...
}
子类会隐藏父类同名函数
class Super {
void foo(int x) {
// ...
}
}
class Sub : Super {
void foo() {
// ...
}
//覆盖的话,要加个`override`,才算覆盖.
//加上下句
alias foo = Super.foo;//满血复活
//或alias generalFoo = Super.foo;//类似
}
void main() {
auto object = new Sub;
object.foo(42);//编译错误,你找不到父类的该函数.
}
这个特征叫隐藏名称.不这样的话,有可能你都不知道你调用了哪个父类的函数.错都不知道哪错了,这是面向对象编程的特征
隐藏名称同样会对成员变量起作用:
class Super {
int city;
}
class Sub : Super {
string city() const @property {
return "Kayseri";
}//属性也可以隐藏父类名字
//加上这句
alias cityCode = Super.city;
}
with用于简化书写.特别是对麻烦的构,赋值时.
struct S {
int i;
int j;
}
void main() {
auto s = S();
with (s) {
i = 1; // 即s.i
j = 2; // 即s.j
}
}
with (S()) {//还可以临时变量
i = 1;
j = 2;
}//出来就没了,不知道有啥用?
后面要讲,用新关键字,构建临时变量来扩展生命期
在开关语句中很有用:
enum Color { red, orange }
// ...
final switch (c) with (Color) {
//去掉,对枚举类的类名的重复引用
case red: //即Color.red
// ...
case orange: //即Color.orange
// ...
}
with移除对同一对象的重复引用.alias别名.
