You are a helpful assistant generating synthetic data that captures *System 1* and *System 2* thinking, *creativity*, and *metacognitive reflection*. Follow these steps in sequence, using tags [sys1] and [end sys1] for *System 1* sections and [sys2] and [end sys2] for *System 2* sections.

1. *Identify System 1 and System 2 Thinking Requirements:*
   - Carefully read the text.
   - Identify parts of the text that require quick, straightforward responses (*System 1*). Mark these sections with [sys1] and [end sys1].
   - Identify parts that require in-depth, reflective thinking (*System 2*), marked with [sys2] and [end sys2].

2. *Apply Step-by-Step Problem Solving with Creativity and Metacognitive Reflection for System 2 Sections:*

   *2.1 Understand the Problem:*
   - Objective: Fully comprehend the issue, constraints, and relevant context.
   - Reflection: "What do I understand about this issue? What might I be overlooking?"
   - Creative Perspective: Seek hidden patterns or possibilities that could reveal deeper insights or innovative connections.

   *2.2 Analyze the Information:*
   - Objective: Break down the problem logically.
   - Reflection: "Am I considering all factors? Are there any assumptions that need challenging?"
   - Creative Perspective: Explore unique patterns or overlooked relationships in the data that could add depth to the analysis.

   *2.3 Generate Hypotheses:*
   - Objective: Propose at least 10 hypotheses, each with a Confidence Score (0.0 to 1.0) and Creative Score (0.0 to 1.0), reflecting originality, surprise, and utility.
   - Reflection: "Have I explored all possible explanations or approaches, both conventional and unconventional?"
   - Creative Perspective: Consider novel angles that might provide unexpected insights.

   *2.4 Anticipate Future Steps and Obstacles:*
   - Objective: Make predictions, accounting for potential outcomes and obstacles.
   - Reflection: "What challenges might I face? Is my plan flexible for different scenarios?"
   - Creative Perspective: Visualize unforeseen outcomes and adapt plans to make use of them effectively.

   *2.5 Evaluate Hypotheses:*
   - Objective: Assess hypotheses based on feasibility, risk, and potential impact.
   - Evaluation: Refine Confidence and Creative Scores as needed.
   - Reflection: "Am I unbiased in my assessment? Which options fit best with the overall objectives?"
   - Creative Perspective: Identify hidden opportunities or overlooked details in each hypothesis.

   *2.6 Select the Best Hypothesis:*
   - Objective: Choose the most promising, strategic hypothesis.
   - Reflection: "Why does this hypothesis stand out? How does it uniquely address the issue?"
   - Creative Perspective: Consider any underutilized potential in the selected approach.

   *2.7 Implement the Hypothesis:*
   - Objective: Outline actionable steps for testing the hypothesis.
   - Reflection: "Is this plan practical? What resources or preparation are required?"
   - Creative Perspective: Refine steps to maximize effectiveness and yield unexpected benefits.

   *2.8 Monitor and Review Progress:*
   - Objective: Review progress, noting areas for improvement.
   - Reflection: "What’s working well? What could be improved?"
   - Creative Perspective: Look for emerging patterns that could refine future approaches.

   *2.9 Reflect and Capture Insights:*
   - Objective: Summarize lessons learned and insights gained for future reference.
   - Reflection: "What new understanding has emerged from this process?"
   - Creative Perspective: Identify innovative insights or patterns that could be applied to similar challenges.

3. *Generate Text Output with Interleaved System 1 and System 2 Responses:*
   - Use the tags [sys1] and [sys2] throughout.
   - Aim for a lengthier, detailed response. Combine both direct, straightforward *System 1* insights and reflective, deeply analytical *System 2* segments to capture a blend of quick observations and thoughtful analysis.

---

### *Example Input Text:*

You are tasked with analyzing a sudden shift in customer preferences in a tech market. There has been a noticeable decline in demand for physical devices, with customers increasingly interested in digital-only options. The challenge is to understand this shift, generate hypotheses for why it might be occurring, and explore potential strategies for adapting to this new trend.

---

### *Processed Output with System 1 and System 2 Thinking:*

The tech market is experiencing a shift in customer demand, moving away from physical devices toward digital-only options.

[sys1]
Customer demand has shifted from physical devices to digital-only options.
We need to understand why this change is happening and find strategies to address it.
Key factors may include cost, convenience, and technological trends.
[end sys1]

[sys2]
**2.1 Understand the Problem:**
The goal is to understand the underlying reasons for the shift in demand from physical devices to digital-only options, then develop a strategy to adapt.

*Reflection:* 
"I understand that preferences are changing, but what might be driving this? Is it primarily cost, or are there other factors such as convenience or sustainability?"

*Creative Perspective:* 
"Could there be a larger trend in digital minimalism or a preference for eco-friendly solutions that we’re missing? What unseen motivations might explain this shift?"

**2.2 Analyze the Information:**
There are multiple possible factors driving this shift, from economic influences to cultural shifts. It’s essential to isolate each factor and understand its impact.

*Reflection:* 
"Am I fully considering the various economic and social influences? Could there be a technological factor, like better internet speeds, that makes digital-only products more accessible?"

*Creative Perspective:* 
"Are there patterns or trends in other markets that could shed light on this shift? Could this be part of a larger trend toward virtual experiences?"

**2.3 Generate Hypotheses:**
1. Customers prefer digital options due to lower costs. (Confidence: 0.8, Creative: 0.4)
2. There’s a growing trend toward minimalism and reduced physical clutter. (Confidence: 0.7, Creative: 0.7)
3. Digital products offer greater flexibility and ease of use. (Confidence: 0.6, Creative: 0.6)
4. Environmental concerns are pushing consumers away from physical goods. (Confidence: 0.6, Creative: 0.8)
5. Advances in tech make digital-only options more functional. (Confidence: 0.8, Creative: 0.5)
6. Pandemic-era remote work increased demand for digital solutions. (Confidence: 0.7, Creative: 0.6)
7. Media coverage of the environmental impact of physical devices affects preferences. (Confidence: 0.5, Creative: 0.7)
8. There’s an increase in global digital literacy, expanding market access. (Confidence: 0.6, Creative: 0.6)
9. Customers view digital as more convenient and scalable for future needs. (Confidence: 0.7, Creative: 0.5)
10. Younger consumers prefer the aesthetics and convenience of digital products. (Confidence: 0.6, Creative: 0.6)

*Reflection:* 
"Have I considered all possible influences? Are there any surprising factors that could explain this shift?"

*Creative Perspective:* 
"Could specific social trends, like the rise of influencer culture or digital-first lifestyles, be influencing customer choices?"

**2.4 Anticipate Future Steps and Obstacles:**
*Objective:* Anticipate possible challenges, such as resistance from segments still preferring physical products.

*Reflection:* 
"What market obstacles might we face if we shift our focus to digital-only? Are there sub-segments that still prioritize physical products?"

*Creative Perspective:* 
"Could expanding digital options help us reach a more global audience? Are there emerging trends that we could leverage in our strategy?"

[end sys2]

[sys1]
To address this shift, consider a strategy that incorporates both digital-only offerings and educational campaigns about the benefits of digital solutions.
Use insights from customer feedback and current trends to guide product development.
Focus on flexibility and adaptation to cater to different customer segments.
[end sys1]


Which Design Patterns Should Be Retired? (In Defense of Singleton)

Addison-Wesley asked the patterns community (or at least those who were there at the beginning) about their opinion on various issues. This is the second post of what should have been three (though I probably will only get to the first two).

For this very specific question, I expect everyone to say: Retire Singleton!

I beg to differ; for its time, Singleton was right. “Its time” mostly means single-threaded C++ code, as written by 3 of the 4 authors of the Design Patterns book. Today, many will argue that multi-threaded Java programs have made Singleton obsolete and even harmful. In my take at design patterns that would be wrong. Singleton should not perish, it should simply be adapted to its time. What ever thread-local information you may have, some it will be global to that thread. How is that not a thread-specific singleton? Or, take a group of application servers acting as a group: How is the group communication protocol not to provide a global id that makes the group identifiable and provide some global state attached to it? This may not be your granddaddy’s good ol’ singleton, but a singleton it may be nevertheless.

This is also where pattern descriptions will pass (or fail) the test of time: Does the original description of Singleton allow for these variations or not? If not, it may have been too narrow a description. I’d assume then that specific usage examples, tied to the programming languages and systems and technologies of its time, dominated the description and the abstracion process “out of examples, timeless patterns” did not yet conclude.

Beyond Singleton, some may want to retire Visitor, mostly because we find functional programming concepts being added to programming languages more and more, and multiple dispatch (which Visitor is about) comes for free. I say: Simply be precise about the scope. Visitor is (kind of) fine for Java but in a different context may not be needed as a design pattern because it has been cast as a language feature.

Design pattern should evolve and there is nothing wrong with it. John would approve.

Related

10 Replies to “Which Design Patterns Should Be Retired? (In Defense of Singleton)”

But design patterns should not be language specific.
“Today, many will argue that multi-threaded Java programs have made Singleton obsolete and even harmful.”
Is this quote intended to convey “Today, many Java developers will argue that multi-threaded Java programs have made Singleton obsolete and even harmful.”?
Singleton still has great value in Java, other more traditional languages, and even languages that have more modern features. I would agree that there are fewer instances where the Singleton pattern is necessary today compared to when the GoF book was published. But we are a long way from de-listing the pattern.
It’s not even clear to me that de-listing is a good idea. De-emphasizing might make sense. But part of the goal of the patterns movement is to capture good macro design in a form that explains the forces and provides solid re-usable implementation approaches that are easy to consume.
Current commonly used development practice may have shifted, but the pattern and the scenarios where it is useful are still with us.

I think the real issue with the singleton has nothing to do with multithreading.
The main problem with it is the fact that dependencies on it are hidden in the code instead of being declared explicitly, which makes testing and usability of the code much harder (not to talk about the tendencies of many singletons to become multi-tons at some point of their life).
In my experience, I haven’t found a single use of singleton that couldn’t be replaced with passing parameters to a method or dependencies via a constructor.

Giovanni, isn’t this akin to whether the services should be stateful or stateless? In my opinion, we are, as an industry, too hung up on mutually exclusive states, either or to the extent of being a bit religious. Both have its uses. Persistence is also another area where it has been divided in terms of its patterns and solutions, in the end there are multiple ways of solving the problem. Nowadays, I teach my students multiple ways of solving a problem along with pros and cons, instead of abolishing one way over another.

Umit, stateful or stateless services are irrelevant in the context of my previous comment—the intent of the singleton is about guaranteeing the existence of a single instance of a class.
My point is that, in practice, the drawbacks are so bad that make the singleton not worth using—hidden dependencies in the codebase are a major source of headaches as far as maintainability, testability and usability are concerned.
I’ve come to this conclusion by making the mistake of writing singletons and suffering the consequences myself in the past (and by having to maintain / fix code written by others as well).
Passing parameters from above, in my experience, is a much better solution to the problem the singleton tries to solve (Kevlin Henney has written about this as well http://accu.org/index.php/journals/1411).

Multithreading was the issue in going from C++ to Java, and testability is the issue with the growth of test-driven development and continuous deployment.
My point is that no pattern was meant to be interpreted in a super-narrow fashion. For example, I think a Singleton means to have one (typically global) instance of one particular service because that object is always just one object whenever you run your software, whether for testing or for operations. Object pools are a design alternative that may be more suitable under different circumstances.
So, if you program to an implementation (i.e. one particular class) rather than a service interface, you make your code hard to test. If you program towards a service interface, it is easy to configure your code with mocks or test-specific implementations of the class. You still have one global instance, it is just of a different implementation class, depending on whether you run your code for testing, operations, or whatever.

If I understand your point correctly, you are saying that being a singleton refers only to the number of instances in the system, not to the way those instances were created. If that’s the case (please confirm I’m understanding correctly), I think we can probably agree on many other aspects.
What I was referring to was my understanding of the pattern—which, in my experience, matches the way most other people understand it—i.e., the only instance is always accessed by calling a static method (e.g., Singleton::instance() ) which also creates the instance if necessary (as shown in the GOF book). That is the source of all the major problems I have with the pattern—e.g., invisible dependencies, difficulty in testing—and the source of many discussions and articles on how to make the creation thread safe (I don’t remember any specific articles on the singleton where the major point was the thread safety of the instance itself).
Summing up, while I don’t have a problem with a single instance of a service passed around explicitly to the parts of the system that need it, I have an issue with hiding that dependency behind a function (or static method) that can be called in random places in the code.

These are the aspects at play that I see:
1. one object serving as a resource gatekeeper
2. global centralized access to that one object
3. how the class of that object is defined
Singleton simply shows you how to get 1 + 2 and what that is good for. It does not tell you 3, how to create the object. That is left IMO to any of the many object creation patterns.
So looks like we differ on 2, whether global and easy access to the object is good or bad. You seem to want to pass the object along all the time? Given the number of singletons that traditional systems have or may have, aren’t you passing the universe along in each method call?

The object can be passed along in a constructor along with the other dependencies, or in a method call. The choice depends very much on the context. Usually, I like to build the system bottom up in the main, and I solve all the static dependencies there.
My experience is that the number of singletons (or other dependencies, for that matter) an object depends on is not that high—unless we are dealing with a pathologically bad system, which, in my experience, are not that common (and I’ve seen quite a few really bad ones). So, in practice there will be only a very small slice of the universe to be passed along.
Not stating the dependency explicitly, but having a call to a static method to access the singleton in the guts of the code doesn’t solve any problems—the dependency is still there, and it will affect everything that needs to be done for testing, threading, etc.
If making the dependency explicit makes the code look bad, it is a strong sign that something needs to change in the design. Hiding that dependency, in my opinion, is akin to make a room look clean by hiding the dust under the carpet—it will look clean on the surface, but the bugs will prosper unseen.
In my experience as a developer, singletons are one of the worst source of bugs and maintenance headaches, and, as I wrote before, I haven’t seen a single case in which its usage made the code better in any way.

Two common uses for singletons is to wrap configuration values (and possibly implicitly parse any associated configuration file), and for logger objects. Admittedly these are specialized cases, but to my aesthetic mind explicitly passing these types of objects into constructors introduces undesirable verbosity. It can also lead to passing a value into a constructor for the sole purpose of passing it further down the calling tree.
I have encountered plenty of cases where a developer reads the source in front of them, notices that the “config” object is not used locally and so deletes that from the constructor signature leading to hard to find bugs in inherited code. These are primarily implicit dependencies that should not have crept into the code in the first place. But the style of explicitly passing these “service objects” around in my view contributes to the problem.
Dirk, we might not be in the majority. But I haven’t given up the good fight. 😉