# Chapter 2. Types

In the previous chapter, we used the data type string to store `Hello, World`. Data types categorize a set of related values, describe the operations that can be done on them, and define the way they are stored. Because types can be a difficult concept to grasp, we will look at them from a couple different perspectives before we see how they are implemented in Go.

Philosophers sometimes make a distinction between types and tokens. For example, suppose you have a dog named Max. Max is the token (a particular instance or member) and dog is the type (the general concept). Dog or dogness describes a set of properties that all dogs have in common. Although oversimplistic, we might reason like this: all dogs have four legs, Max is a dog, therefore Max has four legs. Types in programming languages work in a similar way: all strings have a length, x is a string, therefore x has a length.

In mathematics, we often talk about sets. For example, ℝ (the set of all real numbers) or ℕ (the set of all natural numbers). Each member of these sets shares properties with all the other members of the set. For instance, all natural numbers are associative: “for all natural numbers a, b, and c, a + (b + c) = (a + b) + c and a × (b × c) = (a × b) × c.” In this way, sets are similar to types in programming languages, because all the values of a particular type share certain properties.

Go is a statically typed programming language. This means that variables always have a specific type and ...

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