名字解析 (程序设计)
计算机程序设计语言中，名字解析是指把程序表达式中的标记（）对应解析到程序成分（）。
静态解析与动态解析
编译时完成的称静态名字解析；运行时完成的称动态名字解析。
动态类型并不意味着动态名字解析。例如，Erlang是动态类型但静态名字解析。
下述Python程序:
>>> locals()['num'] = 999 # equivalent to: num = 999
>>> noun = "troubles"
>>> noun2 = "hound"
>>> # which variables to use are decided at runtime
>>> print("{num} {noun} and a {noun2} ain't one".format(**locals()))
999 troubles and a hound ain't one
但现在的编程风格指引不建议使用动态名字解析。[1][2][3]
静态名字解析的语言有：C语言, C++, E语言, Erlang, Haskell, Java, Pascal语言, Scheme语言, Smalltalk。动态名字解析的语言有：Lisp, Perl, PHP, Python, REBOL, Tcl.
名字屏蔽
名字屏蔽（）发生在同一个名字用于不同的实体，出现在重叠的作用域内。 例如，在下述程序中：
private int foo; // A declaration with name "foo" in an outer scope
public void setFoo(int foo) { // A declaration with the same name in the inner scope
// "foo" is resolved by looking in the innermost scope first,
// so the author uses a different syntax, this.foo, to refer to the name "foo"
// in the outer scope.
this.foo = foo;
}
// "foo" here means the same as this.foo below,
// since setFoo's parameter is no longer in scope.
public int getFoo() { return foo; }
α更名简化了名字解析
程序设计语言使用α-变换使得没有变量名屏蔽了其它同名的实体。可用于静态代码分析，使得理解源代码更为容易。
例如：
class Point {
private:
double x, y;
public:
Point(double x, double y) { // x and y declared here mask the privates
setX(x);
setY(y);
}
void setX(double newx) { x = newx; }
void setY(double newy) { y = newy; }
}
Point构造函数中，类的数据成员x与y被局部变量屏蔽了。这可通过α更名改善：
class Point {
private:
double x, y;
public:
Point(double a, double b) {
setX(a);
setY(b);
}
void setX(double newx) { x = newx; }
void setY(double newy) { y = newy; }
}
参考文献
This article is issued from Wikipedia. The text is licensed under Creative Commons - Attribution - Sharealike. Additional terms may apply for the media files.