# Anonymous Functions

Anonymous functions are true to form in that they have *no name*. We've been using them throughout this chapter, but we haven't really talked about them yet.

Anonymous functions are useful when defining a function that will only be used once or to create a quick [closure](https://en.wikipedia.org/wiki/Closure_(computer_programming)).

```go
// doMath accepts a function that converts one int into another
// and a slice of ints. It returns a slice of ints that have been
// converted by the passed in function.
func doMath(f func(int) int, nums []int) []int {
	var results []int
	for _, n := range nums {
		results = append(results, f(n))
	}
	return results
}

func main() {
	nums := []int{1, 2, 3, 4, 5}
	
    // Here we define an anonymous function that doubles an int
    // and pass it to doMath
	allNumsDoubled := doMath(func(x int) int {
	    return x + x
	}, nums)
	
	fmt.Println(allNumsDoubled)
    // prints:
    // [2 4 6 8 10]
}
```

## Assignment

Complete the `printReports` function.

Call `printCostReport` once for each message. Pass in an anonymous function as the `costCalculator` that returns an `int` equal to twice the length of the input message.