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Exercise 1 - Quiz Game

To read a CSV with 2 columns - Question, Answer. Present a quiz to the user, note the answers provided.

Solution:

  • two flags - filename should be able to choose the csv file
  • read the CSV, store the questions in a map[int]Question
  • iterate thru the map, show the question to the user, record the answer
  • in the end, show the score

Exercise 2 - UrlShortner

There are some common names in the http circles for the Go standard libary.

  1. Handler interface
type Handler interface {
	ServeHTTP(ResponseWriter, *Request)
}

A Handler response to the HTTP request. It has the method ServerHTTP, which should write reply headers to the ResponseWriter and then return.

  1. type HandlerFunc

HandlerFunc is a type, which is just a function. This function is just the ServeHTTP function.

// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as HTTP handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler that calls f.
type HandlerFunc func(ResponseWriter, *Request)

// ServeHTTP calls f(w, r).
func (f HandlerFunc) ServeHTTP(w ResponseWriter, r *Request) {
	f(w, r)
}

It’s usecase is this. Let’s say we want to write a function X that can serve requests. One way is to create a new type and make that type have the ServeHTTP method which calls this function X. Or, we can just type cast that function X with http.HandlerFunc(function X) and just use it

  1. ServeMux
// ServeMux is an HTTP request multiplexer.
// It matches the URL of each incoming request against a list of registered
// patterns and calls the handler for the pattern that
// most closely matches the URL.

Unmarshal vs Marshall

Unmarshal is taking in JSON and converting it into structs etc. Marshalling is taking structs and converting them to JSON etc.

Unmarshal parses the JSON-encoded data and stores the result in the value pointed to by v. If v is nil or not a pointer, Unmarshal returns an InvalidUnmarshalError.

Unmarshal uses the inverse of the encodings that Marshal uses, allocating maps, slices, and pointers as necessary, with the following additional rules:

converting a file to []byte

Once we’ve used the os.Open function to read our file into memory, we then have to convert it toa byte array using ioutil.ReadAll.

using var f T vs f := T

One reason you would want to define the type of a variable first and not use := is this:

var f func(string)
f := func(s string) {
    f(s)
}

Here, we have recursive definition of f, which won’t work when we do f:=T