Sorting Room

var x int = 42 // x has type int
f := float64(x) // f has type float64 (ie. 42.0)

import "strconv"

var intString string = "42"
var i, err = strconv.Atoi(intString)

var number int = 12
var s string = strconv.Itoa(number)

var input any = 12
number := input.(int)

str, ok := input.(string) // no panic if input is not a string

var i any = 12 // try: 12.3, true, int64(12), []int{}, map[string]int{}

switch v := i.(type) {
case int:
    fmt.Printf("the integer %d\n", v)
case string:
    fmt.Printf("the string %s\n", v)
default:
    fmt.Printf("type, %T, not handled explicitly: %#v\n", v, v)
}

Instructions

Jen is working in the sorting room in a large factory. The sorting room needs to process anything that comes into it by categorizing it with a label. Jen is responsible for things that were pre-categorized as numbers and needs a program to help her with the sorting.

Most primitive values should get straight-forward labels. For numbers, she wants strings saying "This is the number 2.0" (if the number was 2). Jen wants the same output for integers and floats.

There are a few Box interfaces that need to be unwrapped to get their contents. For a NumberBox, she wants strings saying "This is a box containing the number 3.0" (if the Number() method returns 3). For a FancyNumberBox, she wants strings saying "This is a fancy box containing the number 4.0", but only if the type is a FancyNumber.

Anything unexpected should say "Return to sender" so Jen can send them back where they came from.

1. Describe simple numbers

Jen wants numbers to return strings like "This is the number 2.0" (including one digit after the decimal):

fmt.Println(DescribeNumber(-12.345))
// Output: This is the number -12.3

2. Describe a number box

Jen wants number boxes to return strings like "This is a box containing the number 2.0" (again, including one digit after the decimal):

fmt.Println(DescribeNumberBox(numberBoxContaining{12}))
// Output: This is a box containing the number 12.0

3. Implement a method extracting the number from a fancy number box

Jen needs a helper function to extract the number from a FancyNumberBox. If the FancyNumberBox is a FancyNumber, extract its value and convert it from a string to an int. Any other type of FancyNumberBox should return 0.

fmt.Println(ExtractFancyNumber(FancyNumber{"10"}))
// Output: 10
fmt.Println(ExtractFancyNumber(AnotherFancyNumber{"4"}))
// Output: 0

4. Describe a fancy number box

If the FancyNumberBox is a FancyNumber, Jen wants strings saying "This is a fancy box containing the number 4.0". Any other type of FancyNumberBox should say "This is a fancy box containing the number 0.0".

fmt.Println(DescribeFancyNumberBox(FancyNumber{"10"}))
// Output: This is a fancy box containing the number 10.0
fmt.Println(DescribeFancyNumberBox(AnotherFancyNumber{"4"}))
// Output: This is a fancy box containing the number 0.0

NOTE: we should use the ExtractFancyNumber function!

5. Implement DescribeAnything which uses them all

This is the main function Jen needs which takes any input. DescribeAnything should delegate to the other functions based on the type of the value passed in. More specifically:

• int and float64 should both delegate to DescribeNumber
• NumberBox should delegate to DescribeNumberBox
• FancyNumberBox should delegate to DescribeFancyNumberBox
• anything else should result in "Return to sender"

fmt.Println(DescribeAnything(numberBoxContaining{12.345}))
// Output: This is a box containing the number 12.3
fmt.Println(DescribeAnything("some string"))
// Output: Return to sender