Design pattern--Strategy Mode C + + implementation

Policy Mode C + + implementation 1 definition

(Strategy Pattern) defines a set of algorithms that encapsulate each algorithm and enable them to replace each other.

Also called the policy model

2 class Diagram

3 implementation

Class strategy
{

Protected

Strategy ();

Public

Virtual ~strategy () = 0;

virtual void dosomething () = 0;

};

Class Concretestrategy1:public Strategy

{

Public

void DoSomething ()

{

cout << "Algorithms for Specific Strategy 1" <<endl;

}

};

Class Concretestrategy2:public Strategy

{

Public

void DoSomething ()

{

cout << "Algorithms for Specific Strategy 1" <<endl;

}

};

Encapsulating roles

Class Context

{

Private

Strategy * _STR;

Public

Context (Strategy * st)

: _str (ST)

{}

void Doanything ()

{

_str->dosomething ();

}

};

void Test

{

Strategy * st = new ConcreteStrategy1 ();

Context *con = new context (ST);

Con->doanything ();

}

4 applications

① Advantages

The algorithm is free to switch

Avoid using multiple criteria to judge. Transfer decision-making authority to senior level, you pass in the policy I can do it.

Good extensibility

② Disadvantages

Increased number of strategies

All the strategy classes will be out of the field, the upper level must know the specific strategy

Note: This drawback is can be remedied by other means eg factory method, proxy mode, enjoy meta mode

5 Usage Scenarios

Multiple classes are only slightly different on the algorithm

The algorithm needs to switch freely

Where the algorithm rules need to be masked. (Analogous function)

Note, a policy family should not have more than 4 specific policies, or use mixed mode to solve the problem of policy class expansion and external storm drain.

6 extensions

Enumeration policy

Definition: It is an enumeration that concentrates the enumeration of policy patterns

Enumeration attributes: Pubic,finaly,static

So in C + + it is actually a class that encapsulates multiple static methods. (half used as a role that does not change frequently)

eg Strategy::add ();

Strategy::sub (); .....

Design pattern--Strategy Mode C + + implementation