Functions: Syntax and Return Types

A function is a reusable block of code designed to perform a specific task. Functions prevent code duplication, help organize code into logical modules, and make programs easier to test.

Dart is a true object-oriented language, meaning functions are objects and have a type (Function). This allows functions to be assigned to variables or passed as arguments.

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Basic Function Syntax

A standard Dart function consists of a return type, a descriptive name, a parameter list enclosed in parentheses, and a body enclosed in curly braces.

dart
ReturnType functionName(ParameterType parameter1, ParameterType parameter2) {
  // Function body
  return value;
}

If you do not specify a return type, Dart defaults to dynamic, but you should always explicitly annotate return types for clean code.

dart
// Example function returning an integer
int add(int a, int b) {
  return a + b;
}

// Example function returning nothing (void)
void greet(String name) {
  print("Hello, $name!");
}

void main() {
  int result = add(5, 3);
  print(result); // 8
  greet("Alice"); // Hello, Alice!
}

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Return Types in Dart

Functions can return any valid type in Dart.

• void: Indicates that the function does not return a value. If a function reaches the end of its body without a return statement, it implicitly returns null.
• Primitive Types: int, double, String, bool.
• Collections: List, Set, Map.
• Objects: Custom class instances.
• Never: Indicates that the function never returns (e.g., it always throws an exception).

dart
List<String> getRoles() {
  return ["Admin", "User", "Guest"];
}

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Single-Expression Functions (Arrow Syntax)

For functions that contain only a single expression (a single line of code that evaluates to a value), Dart provides a shorthand arrow syntax (=>).

dart
// Standard syntax
int square(int number) {
  return number * number;
}

// Arrow syntax equivalent
int squareArrow(int number) => number * number;

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Summary

• Functions group reusable code blocks.
• Explicitly declare the return type and parameter types to catch errors early.
• Use void if the function does not return a value.
• Use the arrow syntax (=>) shorthand for simple, single-expression functions.