When our application is running in production, it will receive many requests with short URLs, and several requests to turn a long URL into a short one. But, which data structure will our program stock this data in?

Both URL-types (A) and (B) from the last lesson are strings. Moreover, they relate to each other: given (B) as a key, we need to fetch (A) as its value, i.e., they map to each other. To store our data in memory, we need such a map structure, a map[string]string. The key type is written between [ ], and the value type follows, as we learned all about maps in Chapter 6. In any non-trivial program, it is useful to give the special types that you use a name. In Go, we do this with the keyword type, so we define a: type URLStore map[string]string. It maps short URLs to long URLs; both are strings.

To make a variable of that type named urls, just use: urls := make(URLStore). Suppose we want to store the mapping of http://goto/a to http://google.com/ in urls; we can do this with the statement:

urls ["a"] = "http://google.com/"

We just store the suffix of http://goto/ as a key, and what comes before the key is a fixed URL prefix.

To retrieve its corresponding long URL given “a”, we write:

url := urls ["a"]

Then, the value of url is equal to “http://google.com/”. Note that with := we don’t need to say that url is of type string; the compiler deduces the type from the value on the right side.

Making it thread-safe

Our URLStore variable is the central memory data store here. Once we get some traffic, there will be many ...

Setting up the Structure of Application