Transform scattered inputs into one clear object Transform scattered inputs into one clear object TL;DR: Wrap messy parameters into a single meaningful entity. TL;DR: Wrap messy parameters into a single meaningful entity. Problems Addressed 😔 Parameter overload
Order confusion
Anemic Models
Low readability
Hard extension
DTOs
Weak semantics
Repeated validations
Accidental argument swapping
Primitive Obsession
Data Clumps
Weak type safety
Missing Small Objects
Missing Intervals Parameter overload overload Order confusion Order confusion Anemic Models Anemic Models Low readability Hard extension DTOs DTOs Weak semantics Repeated validations validations Accidental argument swapping argument swapping Primitive Obsession Primitive Obsession Data Clumps Data Clumps Weak type safety Missing Small Objects Small Objects Missing Intervals Intervals Related Code Smells 💨 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xviii https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xviii https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-ii-o96s3wl4 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-ii-o96s3wl4 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxvi https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxvi https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxix https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxix https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-x-i7r34uj https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-x-i7r34uj https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxix https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxix https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-viii-8mn3352 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-viii-8mn3352 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-i-xqz3evd https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-i-xqz3evd https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxviii https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxviii https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xix https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xix https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-iv-7sc3w8n https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-iv-7sc3w8n Steps 👣 Identify multiple parameters of the same type
Create a meaningful entity to group them
Add missing validation rules to fail fast
Replace function signatures with the new entity
Adjust all callers to pass the entity
Add context-specific names to improve clarity Identify multiple parameters of the same type Create a meaningful entity to group them Add missing validation rules to fail fast Replace function signatures with the new entity Adjust all callers to pass the entity Add context-specific names to improve clarity Sample Code 💻 Before  🚨 function findHolidays(
 maxPrice: Currency, 
 startDate: Date,
 endDate: Date, 
 minPrice: Currency) {
  // Notice that maxPrice and minPrice are swapped by mistake
  // Also, dates are mixed
} function findHolidays(
 maxPrice: Currency, 
 startDate: Date,
 endDate: Date, 
 minPrice: Currency) {
  // Notice that maxPrice and minPrice are swapped by mistake
  // Also, dates are mixed
} After 👉 // 2. Create a meaningful entity to group them  

class PriceRange {
  constructor(public min: Currency, public max: Currency) {
    if (min > max) {
      throw new Error(
        `Invalid price range: min (${min}) `+
        `cannot be greater than max (${max})`
      );
    }
    if (min < 0) {
      throw new Error(
        `Invalid price range: min (${min}) cannot be negative`);
    }
  }
}

class Interval {
  // 3. Add missing validation rules to fail-fast
  constructor(public start: Date, public end: Date) {
    if (start > end) {
      throw new Error(
        `Invalid date range: start (${start.toISOString()})  ` + 
        `cannot be after end (${end.toISOString()})`
      );
    }
  }
}

class HolidaySearchCriteria {
  constructor(
    public priceRange: PriceRange,
    public dateRange: Interval
  ) {}
}

function findHolidays(criteria: HolidaySearchCriteria): Holiday[] {
  // 1. Identify multiple parameters of the same type  
  // No need to call validate() - already validated in constructors
  // 4. Replace function signatures with the new entity  
  const { priceRange, dateRange } = criteria;
  // 5. Adjust all callers to pass the entity  
  // 6. Add context-specific names to improve clarity 
  
  return database.query({
    price: { $gte: priceRange.min, $lte: priceRange.max },
    startDate: { $gte: dateRange.start },
    endDate: { $lte: dateRange.end }
  });
}
 
try {
  const criteria = new HolidaySearchCriteria(
    new PriceRange(500, 1000),  // ✅ Valid
    new Inteval(
      new Date('2025-06-01'), 
      new Date('2025-06-15')
    )
  );
  
  findHolidays(criteria);
  
  // ❌ This will throw immediately
  // Great for UI and API validation
  new PriceRange(1000, 500);
  
} catch (error) {
  console.error(error.message);
} // 2. Create a meaningful entity to group them  

class PriceRange {
  constructor(public min: Currency, public max: Currency) {
    if (min > max) {
      throw new Error(
        `Invalid price range: min (${min}) `+
        `cannot be greater than max (${max})`
      );
    }
    if (min < 0) {
      throw new Error(
        `Invalid price range: min (${min}) cannot be negative`);
    }
  }
}

class Interval {
  // 3. Add missing validation rules to fail-fast
  constructor(public start: Date, public end: Date) {
    if (start > end) {
      throw new Error(
        `Invalid date range: start (${start.toISOString()})  ` + 
        `cannot be after end (${end.toISOString()})`
      );
    }
  }
}

class HolidaySearchCriteria {
  constructor(
    public priceRange: PriceRange,
    public dateRange: Interval
  ) {}
}

function findHolidays(criteria: HolidaySearchCriteria): Holiday[] {
  // 1. Identify multiple parameters of the same type  
  // No need to call validate() - already validated in constructors
  // 4. Replace function signatures with the new entity  
  const { priceRange, dateRange } = criteria;
  // 5. Adjust all callers to pass the entity  
  // 6. Add context-specific names to improve clarity 
  
  return database.query({
    price: { $gte: priceRange.min, $lte: priceRange.max },
    startDate: { $gte: dateRange.start },
    endDate: { $lte: dateRange.end }
  });
}
 
try {
  const criteria = new HolidaySearchCriteria(
    new PriceRange(500, 1000),  // ✅ Valid
    new Inteval(
      new Date('2025-06-01'), 
      new Date('2025-06-15')
    )
  );
  
  findHolidays(criteria);
  
  // ❌ This will throw immediately
  // Great for UI and API validation
  new PriceRange(1000, 500);
  
} catch (error) {
  console.error(error.message);
} Type 📝 Semi-Automatic Semi-Automatic Safety 🛡️ Many IDEs support this pattern. Why is the Code Better? ✨ You avoid order confusion and increase readability. You make functions easy to extend with new parameters. You bring semantic meaning to the input data. You eliminate the risk of passing arguments in the wrong order since the object properties have explicit names. You make function calls self-documenting because each value clearly indicates its purpose. You simplify adding new optional parameters without breaking existing code. You enable better IDE support with autocomplete showing parameter names. You create opportunities to reuse the parameter object type across related functions. reuse the parameter object type You fail fast, asserting on the relations among parameters. fail fast How Does it Improve the Bijection? 🗺️ You move closer to a one-to-one map between the business concept of a "search request" and your code model. one-to-one map You stop treating the data as loose numbers and give them an explicit identity that matches the domain. explicit identity In the real world, you describe searches using named criteria rather than ordered lists. When you ask someone to "search for products with a minimum price of 50 and a maximum price of 100," you use named concepts. This refactoring mirrors that natural language structure in your code. language structure The SearchCriteria becomes a first-class concept that maps directly to how searching works in the real world. SearchCriteria maps Refactor with AI 🤖 Ask AI to scan your codebase for functions that use two or more parameters of the same type. Instruct it to propose an entity name, generate the type or class, and rewrite both the function and its callers to use the new entity. Suggested Prompt: 1. Identify multiple parameters of the same type  2. Create a meaningful entity to group them  3. Add missing validation rules to fail fast 4. Replace function signatures with the new entity  5. Adjust all callers to pass the entity  6. Add context-specific names to improve clarity Suggested Prompt: 1. Identify multiple parameters of the same type  2. Create a meaningful entity to group them  3. Add missing validation rules to fail fast 4. Replace function signatures with the new entity  5. Adjust all callers to pass the entity  6. Add context-specific names to improve clarity Without Proper Instructions

With Specific Instructions



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Claude



Perplexity

Perplexity



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Copilot



You

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Gemini

Gemini



DeepSeek

DeepSeek



Meta AI

Meta AI



Grok

Grok



Qwen

Qwen Without Proper Instructions

With Specific Instructions



ChatGPT

ChatGPT



Claude

Claude



Perplexity

Perplexity



Copilot

Copilot



You

You



Gemini

Gemini



DeepSeek

DeepSeek



Meta AI

Meta AI



Grok

Grok



Qwen

Qwen Without Proper Instructions

With Specific Instructions Without Proper Instructions Without Proper Instructions With Specific Instructions With Specific Instructions ChatGPT

ChatGPT ChatGPT ChatGPT ChatGPT ChatGPT ChatGPT ChatGPT Claude

Claude Claude Claude Claude Claude Claude Claude Perplexity

Perplexity Perplexity Perplexity Perplexity Perplexity Perplexity Perplexity Copilot

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Qwen Qwen Qwen Qwen Qwen Qwen Qwen Tags 🏷️ Primitive Obsession Primitive Obsession Level 🔋 [x]Intermediate [x]Intermediate [x] Related Refactorings 🔄 https://refactoring.guru/es/introduce-parameter-object?embedable=true https://refactoring.guru/es/introduce-parameter-object?embedable=true https://hackernoon.com/refactoring-013-eliminating-repeated-code-with-dry-principles?embedable=true https://hackernoon.com/refactoring-013-eliminating-repeated-code-with-dry-principles?embedable=true https://hackernoon.com/refactoring-019-how-to-reify-email-addresses?embedable=true https://hackernoon.com/refactoring-019-how-to-reify-email-addresses?embedable=true Also known as https://refactoring.guru/es/introduce-parameter-object?embedable=true https://refactoring.guru/es/introduce-parameter-object?embedable=true Credits 🙏 Image by Gerd Altmann on Pixabay Gerd Altmann Pixabay This article is part of the Refactoring Series. https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true https://maximilianocontieri.com/how-to-improve-your-code-with-easy-refactorings?embedable=true

The code in this story is for educational purposes. The readers are solely responsible for whatever they build with it.

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