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for_in

The for...in loop is the most idiomatic way to iterate over collections in Soul. It provides a clean syntax for iterating through lists, maps, and other iterable objects without managing indices manually.

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Basic For-In with Lists

Iterate through list elements: 
fruits = ["apple", "banana", "cherry", "date"]

for (fruit in fruits) {
    println("Fruit: " + fruit)
}
// Output: apple, banana, cherry, date

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For-In with Maps

Iterate through map key-value pairs: 
user = {
    "name": "Alice",
    "age": 30,
    "city": "New York"
}

for (key, value in user) {
    println(key + ": " + value)
}
// Output: name: Alice, age: 30, city: New York

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For-In with Key Only (Maps)

Iterate through map keys only: 
config = {
    "debug": true,
    "timeout": 5000,
    "retries": 3
}

for (key in config) {
    println("Setting: " + key + " = " + config[key])
}

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For-In with Value Only (Lists)

The standard pattern for lists: 
numbers = [1, 2, 3, 4, 5]

for (num in numbers) {
    result = num * 2
    println("Double: " + result)
}

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For-In with Index and Value

Some collections may provide both index and value: 
items = ["first", "second", "third"]

for (index, item in items) {
    println("Index " + index + ": " + item)
}

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For-In with Nested Collections

Iterate through nested data structures: 
users = [
    {"name": "Alice", "age": 25},
    {"name": "Bob", "age": 30},
    {"name": "Charlie", "age": 35}
]

for (user in users) {
    println("User: " + user.name + " (Age: " + user.age + ")")
}

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For-In with String Characters

Iterate through string characters: 
text = "Hello"

for (char in text) {
    println("Character: " + char)
}
// Output: H, e, l, l, o

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For-In with Break and Continue

Control loop execution: 
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

for (num in numbers) {
    if (num == 5) {
        break  // Exit when number is 5
    }
    
    if (num % 2 == 0) {
        continue  // Skip even numbers
    }
    
    println("Odd number: " + num)
}
// Output: 1, 3

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For-In with Complex Data

Process complex data structures: 
orders = [
    {"id": 1, "customer": "Alice", "total": 150.00},
    {"id": 2, "customer": "Bob", "total": 75.50},
    {"id": 3, "customer": "Charlie", "total": 200.00}
]

totalRevenue = 0

for (order in orders) {
    totalRevenue += order.total
    println("Order " + order.id + ": $" + order.total)
}

println("Total Revenue: $" + totalRevenue)

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For-In with Filtering

Filter elements during iteration: 
products = [
    {"name": "Laptop", "price": 999, "category": "Electronics"},
    {"name": "Book", "price": 15, "category": "Literature"},
    {"name": "Phone", "price": 599, "category": "Electronics"}
]

for (product in products) {
    if (product.category == "Electronics") {
        println("Electronic: " + product.name + " - $" + product.price)
    }
}

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For-In with Transformations

Transform data during iteration: 
names = ["alice", "bob", "charlie"]
capitalizedNames = []

for (name in names) {
    capitalizedName = name.toUpperCase()
    capitalizedNames.push(capitalizedName)
}

for (name in capitalizedNames) {
    println("Capitalized: " + name)
}

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For-In with Function Calls

Call functions for each element: 
soul processUser(user) {
    return "Processed: " + user.name + " (" + user.email + ")"
}

users = [
    {"name": "Alice", "email": "alice@example.com"},
    {"name": "Bob", "email": "bob@example.com"}
]

for (user in users) {
    result = processUser(user)
    println(result)
}

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For-In with Maps and Complex Keys

Iterate through maps with complex structures: 
cache = {
    "user:123": {"name": "Alice", "lastSeen": "2023-01-01"},
    "user:456": {"name": "Bob", "lastSeen": "2023-01-02"},
    "user:789": {"name": "Charlie", "lastSeen": "2023-01-03"}
}

for (key, userData in cache) {
    println("Key: " + key)
    println("User: " + userData.name + " (Last seen: " + userData.lastSeen + ")")
}

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For-In with Nested Loops

Nested for-in loops for multi-dimensional data: 
departments = {
    "Engineering": ["Alice", "Bob", "Charlie"],
    "Marketing": ["Dave", "Eve"],
    "Sales": ["Frank", "Grace", "Henry"]
}

for (department, employees in departments) {
    println("Department: " + department)
    
    for (employee in employees) {
        println("  Employee: " + employee)
    }
}

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For-In with Error Handling

Handle errors during iteration: 
urls = ["http://example1.com", "http://example2.com", "invalid-url"]

for (url in urls) {
    try {
        response = fetchData(url)
        println("Success: " + url)
    } catch (error) {
        println("Error with " + url + ": " + error)
    }
}

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For-In with Conditional Logic

Complex conditional processing: 
students = [
    {"name": "Alice", "grade": 85, "subject": "Math"},
    {"name": "Bob", "grade": 92, "subject": "Science"},
    {"name": "Charlie", "grade": 78, "subject": "Math"}
]

for (student in students) {
    if (student.subject == "Math" && student.grade >= 80) {
        println("Honor student: " + student.name + " (Grade: " + student.grade + ")")
    }
}

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For-In with Accumulation

Accumulate values during iteration: 
expenses = [
    {"category": "Food", "amount": 50},
    {"category": "Transport", "amount": 30},
    {"category": "Food", "amount": 25},
    {"category": "Entertainment", "amount": 40}
]

categoryTotals = {}

for (expense in expenses) {
    category = expense.category
    amount = expense.amount
    
    if (categoryTotals[category] == null) {
        categoryTotals[category] = 0
    }
    
    categoryTotals[category] += amount
}

for (category, total in categoryTotals) {
    println(category + ": $" + total)
}

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For-In Performance Tips

Optimize for-in loop performance: 
// Cache expensive operations outside the loop
items = getItems()
processor = createProcessor()

for (item in items) {
    processor.process(item)  // Reuse processor
}

// Avoid creating objects in loops
for (item in items) {
    // Good - reuse variables
    result = processItem(item)
    
    // Avoid - creates new object each iteration
    // config = {"setting": "value"}
}

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Best Practices

  1. Use for-in for collections: It’s more readable than index-based loops
  2. Use meaningful variable names: user instead of u
  3. Handle null/undefined: Check for valid data before processing
  4. Use break/continue appropriately: Control flow when needed
// Good - clear and safe
soul processValidUsers(users) {
    if (users == null) {
        return
    }
    
    for (user in users) {
        if (user == null || !user.isActive) {
            continue
        }
        
        processUser(user)
    }
}

// Better - with error handling
soul processValidUsers(users) {
    if (users == null || users.length() == 0) {
        return
    }
    
    for (user in users) {
        try {
            if (user != null && user.isActive) {
                processUser(user)
            }
        } catch (error) {
            println("Error processing user: " + error)
        }
    }
}
The for...in loop is the preferred way to iterate over collections in Soul, providing clean, readable code that’s less error-prone than manual index management.
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