C + + Implements Builder mode through internal classes

There is a good way to implement the builder pattern in Java. The builder mode is implemented here using C + + in the Java version.

In C + +, inner and outer classes are not directly related, and private objects of external classes cannot be accessed through an inner class, nor can private objects of inner classes be accessed through external classes. So the Friend keyword is used here to enhance the internal class's access to external classes, primarily by accessing the private constructors of the external classes. The code is as follows:

#include <iostream>#include<memory>using namespacestd;classbuilderdemo{ Public:    classBuilder { Public:        intservingsize; intservings; Builder (intServingsize,intservings): Servingsize (Servingsize), servings (servings) {} shared_ptr<BuilderDemo>build () {returnShared_ptr<builderdemo> (NewBuilderdemo (* This));    }    }; Private: Builderdemo (Constbuilder&builder) {Servingsize=builder.servingsize; Servings=builder.servings; } friendclassBuilder; Private:    intservingsize; intservings;};intMain () {Builderdemo::builder Builder (4, +); shared_ptr<BuilderDemo> demo =builder.build ();}

Some of the member variables of the external class are omitted here, and in general the builder mode can be used when the number of member variables for an external class is more than 4.

C + + Implements Builder mode through internal classes