String Interpolation

String interpolation is a powerful feature in Dart that allows you to embed expressions and variables directly inside strings. Think of it as a way to "inject" values into your strings without having to concatenate them manually!

Basic String Interpolation

In Dart, you use the $ symbol followed by a variable name to interpolate simple variables:

void main() {
  String name = 'Alice';
  int age = 25;
  
  print('Hello, my name is $name and I am $age years old.');
  // Output: Hello, my name is Alice and I am 25 years old.
}

Expression Interpolation

For more complex expressions, you wrap them in curly braces ${}:

void main() {
  int length = 10;
  int width = 5;
  
  print('The area of the rectangle is ${length * width} square units.');
  // Output: The area of the rectangle is 50 square units.
  
  String firstName = 'John';
  String lastName = 'Doe';
  
  print('Full name: ${firstName.toUpperCase()} ${lastName.toUpperCase()}');
  // Output: Full name: JOHN DOE
}

When to Use Curly Braces

Use $variable	Use ${expression}
Simple variable names	Complex expressions
$name, $age	${name.length}, ${x + y}
No method calls	Method calls like ${text.toUpperCase()}
No operators	Mathematical operations like ${a * b}

Practical Examples

Here are some common use cases for string interpolation:

void main() {
  // Working with numbers
  double price = 29.99;
  int quantity = 3;
  print('Total cost: \$${(price * quantity).toStringAsFixed(2)}');
  // Output: Total cost: $89.97
  
  // Working with lists
  List<String> fruits = ['apple', 'banana', 'orange'];
  print('I have ${fruits.length} fruits: ${fruits.join(', ')}');
  // Output: I have 3 fruits: apple, banana, orange
  
  // Conditional expressions
  int score = 85;
  print('Result: ${score >= 60 ? 'Pass' : 'Fail'}');
  // Output: Result: Pass
}

Why Use String Interpolation?

String interpolation makes your code:

• More readable: Compare 'Hello $name' vs 'Hello ' + name
• More efficient: Dart optimizes interpolated strings
• Less error-prone: No need to worry about missing spaces or plus signs

It's like having a template where you can fill in the blanks with actual values - much cleaner than gluing strings together piece by piece!