Joe Wood Notes

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Function Definition with Arguments and Return Type

Golang requires explicit type declarations for function parameters and return values.

func add(x int, y int) int {
    return x + y
}

func greet(name string) string {
    return fmt.Sprintf("Hello, %s!", name)
}

• Parameters and return types are explicitly defined.
• Multiple parameters of the same type can be grouped: func add(x, y int) int.
• Functions can return multiple values.

func divide(a, b int) (int, int) {
    return a / b, a % b
}

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Function Overloading

No function overloading, but can emulate it with interfaces

import (
    "fmt"
)

func Add(x, y interface{}) interface{} {
    switch x.(type) {
    case int:
        return x.(int) + y.(int)
    case string:
        return x.(string) + y.(string)
    default:
        return nil
    }
}

func main() {
    fmt.Println(Add(5, 10))          // 15
    fmt.Println(Add("Hello, ", "World!"))  // "Hello, World!"
}

---

Default Arguments

Not supported by Go, but you can use variadic parameters

func greet(name string, greetings ...string) {
    greeting := "Hello"
    if len(greetings) > 0 {
        greeting = greetings[0]
    }
    fmt.Printf("%s, %s!\n", greeting, name)
}

func main() {
    greet("Alice", "Hi")  // Uses "Hi"
    greet("Bob")          // Uses default "Hello"
}

Or simulate it with a struct:

type Config struct {
    Greeting string
    Name     string
}

func greet(cfg Config) {
    greeting := cfg.Greeting
    if greeting == "" {
        greeting = "Hello"
    }
    fmt.Printf("%s, %s!\n", greeting, cfg.Name)
}

func main() {
    greet(Config{Name: "Alice", Greeting: "Hi"})
    greet(Config{Name: "Bob"}) // Greeting defaults to "Hello"
}

---

Lambda Function

In Go, lambda functions (also called anonymous functions) are defined inline without a name and can be immediately invoked or assigned to a variable.

Example:

func main() {
    // Immediately invoked function
    func() {
        fmt.Println("Hello from a lambda function!")
    }()

    // Assigning a lambda function to a variable
    add := func(a, b int) int {
        return a + b
    }

    fmt.Println("Sum:", add(3, 4)) // Output: Sum: 7
}

---

Lambda Functions Capturing Values

Lambda functions in Go capture variables from their surrounding scope by reference, meaning changes in the function affect the original variable.

Example:

func main() {
    x := 10

    // Lambda function capturing 'x' from outer scope
    modifyX := func() {
        x += 5 // Modifies x from the outer scope
    }

    modifyX() // Call lambda function
    fmt.Println("Modified x:", x) // Output: Modified x: 15
}

However, since Go passes function parameters by value (unless using pointers), lambda functions do not automatically modify arguments unless explicitly passed by reference:

func main() {
    x := 10

    // Lambda function that takes an argument (no capture)
    increment := func(n int) {
        n += 5 // This modifies only the local copy of 'n'
    }

    increment(x)
    fmt.Println("Unchanged x:", x) // Output: Unchanged x: 10
}

To modify x, pass it by reference using a pointer:

func main() {
    x := 10
    // Lambda function using pointer to modify the actual variable
    increment := func(n *int) {
        *n += 5
    }
    increment(&x)
    fmt.Println("Modified x:", x) // Output: Modified x: 15
}

---

Function Generics

import "fmt"

func identity[T any](value T) T {
    return value
}

func main() {
    fmt.Println(identity(42))       // 42
    fmt.Println(identity("Hello"))  // Hello
}

---

Function Generics with Constraints

And with constraints:

import "fmt"

// Constraint: only types that support the + operator
type Number interface {
    int | float64
}

func add[T Number](a, b T) T {
    return a + b
}

func main() {
    fmt.Println(add(5, 10))      // 15
    fmt.Println(add(5.5, 2.3))   // 7.8
}