README.md

List of Keys

Slices

A Go slice is a sequence of typed data

names := []string{"bugs", "daffy", "elmer"}

We can use slicing on slices

fmt.Println(names[1:])

To add values, use append

names = append(names)

for Loops

The only iteration mechanism in Go is the for loop.

We can use for like we do in many other languages

for i := 0; i < 3; i++ {
	fmt.Println(i)
}

We can use it as a while loop

n := 3
for n > 0 {
	fmt.Println(n)
	n--
}

Also as an infinite loop

j := 0
for {
	fmt.Println(j)
	j++
	if j > 2 {
		break // Stop the loop
	}
}

To help avoid making off-by-one errors, we have range.

range in single value context will go over indices

s := "abc"
for i := range s {
	fmt.Println(i)
}

range in double value context will go over indices & values

for i, c := range s {
	fmt.Println(i, c)
}

The Empty Interface

Go is a typed language. In some ways it's more strict than C/Java - for example you can't divide a integer with a float. However sometimes we'd like a variable that holds any type (object in Java, void * in C/C++ ...). In Go this type is the empty interface, which is written as interface{}.

var i interface{}

i = 10

// Print value and type
fmt.Printf("%v (%T)\n", i, i) // 10 (int)

i = "hello"
fmt.Printf("%v (%T)\n", i, i) // hello (string)

JSON

JSON is a very common serialization format used in REST APIs. Go has JSON encoders and decoders that will take a Go data structure and convert it to/from a byte slice.

Since JSON objects (Go maps or structs) can hold different types, we'll be using interface{}

data := map[string]interface{}{
	"name": "daffy",
	"age":  80,
}

enc := json.NewEncoder(os.Stdout) // Encode to standard output
if err := enc.Encode(data); err != nil {
	fmt.Printf("error: can't encode - %s\n", err)
}

Exercise

Add a /keys entry point which will return all the keys in the database as a JSON array in an object (see below).

Testing

curl http://localhost:8080/keys

{
"keys": ["x", "y"]
}

Solution