kandi X-RAY | DesignPattern Summary
kandi X-RAY | DesignPattern Summary
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Trending Discussions on DesignPattern
In the Head First Design Patterns book, the authors describe using an iterator to traverse over composite data structures. They provide some sample code which, when executed, prints out a series of menu items stored within the composite. However, if you try to call the iterator more than once, it no longer works as expected and won't produce any results. The following code appears to be causing the problem:...
ANSWERAnswered 2021-Mar-18 at 13:51
As the linked issue says in the comments:
I am learning design pattern in python and the subject is singleton objects so, I was writing my main code as
PRO003 and import it into
PRO004. This is
ANSWERAnswered 2021-Jan-29 at 08:07
__SingletonObject is not be instantiated
I just want a quick lookover that I implemented the different fly strategies correctly.
The program simply consists of a duck class that uses an interface for its fly method. The interface has different implementations (namely SimpleFly and NoFly), and a switch statement chooses the correct method based on the specie enum.
As I understand, the strategy pattern is meant to avoid duplicate code between child classes at the same level, which decreases maintainability and extensibility. So instead we abstract out the related algorithms to interfaces and choose them as needed.
ANSWERAnswered 2020-Dec-18 at 20:48
I would point out a couple issues of semantics and terminology.
- It's confusing to have a method named
flythat can be implemented as not flying. Naming the method
tryToFlyor documenting the method as merely an attempt are two ways of addressing this confusion. The software principle to reference here is Liskov Substitution.
- The base class does not implement one of the strategies; rather, it composes a strategy. The purpose of the Strategy pattern is to avoid subclassing through composition.
- To reiterate one of the comments,
Duckshould accept an instance of
IFlydirectly in its constructor (or a setter method) rather than switching on an enum. Another goal of the Strategy pattern is to avoid branching logic.
The essence of the pattern is that you've avoided creating multiple subclasses of
Duck by instead creating multiple implementations of
IFly. This has the advantage that those
IFly implementations can be reused without a complex inheritance hierarchy, e.g.
CITY can share one strategy.
As mentioned in the comments, strategies also have the advantage that a
Duck could change its strategy at runtime. For example,
IFly might be implemented by
Glide so that a
Duck would switch between these different strategies depending on the wind.
I am playing with php 7 and phpunit 6. Here is the test I wrote:...
ANSWERAnswered 2017-Feb-14 at 11:16
I found the answer:
I was excuting my test with this command line:
I use a
LocalContainerEntityManagerFactoryBean to setting up a JPA
Among the scanned entities I scan with
setPackagesToScan I have a User entity that implement spring security interface
When I lunch my application I have this error:...
ANSWERAnswered 2019-Jun-05 at 13:20
I bypassed the problem by removing the implementation of the
UserDetails interface from my
User entity, and set up a new mechanism to recover the
GrantedAuthority necessary for Spring Security.
But I still do not understand why this interface implementation poses a problem with
setPackagesToScan used by the JPA
If somone can give us an explanation?
I am trying to
make_pair with a unique_ptr like in the example below
(The code is a C++ implementation of the Facade Design pattern)...
ANSWERAnswered 2018-Jun-30 at 15:08
Is this due to the old version of G++ shipped by Apple?
No. It is because you are trying to copy the unique pointer by passing it to
std::unique_ptr is not copyable. In fact it is move-only. Change to:
I am trying to test the method:...
ANSWERAnswered 2018-Feb-25 at 19:32
I'd follow the XP rule of doing the simplest thing that could possibly work. You don't need to mock anything, so just use the objects directly.
I am trying to make a class
ShapeManager which is instantiated only once, and have a base class
Shape(and all of its children) have access to it. This would result in a structure that looks like this:
ANSWERAnswered 2018-Jan-31 at 03:26
Don't try and make a global variable accessible through all your code. Make a certain object accessible only to who needs it. Thus, make a private
ShapeManager in Shape and pass it through
But it's still strange that
Shape has to have access to
EDIT - Comment by the author: My main motivation to creating a ShapeManager is to store a reference to m_shapes, m_world, and m_gen, but i didn't want every shape object to have those 3 reference variables.
You can have a struct that stores your 3 reference variables and each object that needs access to them would have a private struct.
Some other file:
I am from C++ background, recently started learning Design Patterns.
I am facing problems with this code from Head First Design Patterns:
ANSWERAnswered 2017-Nov-28 at 15:19
PizzaStore class already contains a SimplePizzaFactory object
Well, PizzaStore have a non-initialized attribute of type SimplePizzaFactory. In the PizzaStore constructor, that attribute is initialized with a reference to the constructor argument. This is an usual pattern in Java code.
The passed-on object is not initialized with any data (which needs to be copied by PizzaStore Constructor)
There is no need to add initialization code in the constructor, is asumed that the SimplePizzaFactory is already initialized. That factory is not copied, is referenced by the PizzaStore attribute, so the factory inside the PizzaStore, after the constructor is executed, is an already initialized object.
I want to create Collection of stubs so that first Item when I call getId() method return 0, second Item.getId() return 1 and so on. Value of getId() method must be equal index of element. I try this...
ANSWERAnswered 2017-Jun-05 at 16:06
What you need to do is to mock
Item as well.
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