Overview of Data Types

Types

Variables contain data, and data can be of different data types or types for short. Go is a statically typed language. It means the compiler must know the types of all the variables, either because they were explicitly indicated, or because the compiler can infer the type from the code context. A type defines the set of values and the set of operations that can take place on those values. Here is an overview of some categories of types:

A structured type, which has no real value (yet), has the value nil, which is also the default value for these types. To declare a variable, var keyword is used as:

var var1 type1

var1 is the variable name, and type1 is the type of var1.

Functions can also be of a certain type. The (return) type of function is the type of variable which is returned by it. This type is written after the function name and its optional parameter-list, like:

func FunctionName (a typea, b typeb) typeFunc

So, you can see that typeFunc is the (return) type of the function, FunctionName. The returned variable var1 of type typeFunc appears somewhere in the function in the statement as:

return var1

A function can have more than one return variables. In this case, the return-types are separated by comma(s) and surrounded by ( ), like:

func FunctionName (a typea, b typeb) (t1 type1, t2 type2)

Two variables are returned with type type1 and type2 respectively. For such a case, the return statement takes the form:

return var1, var2

We can also have user-defined data types (our own data types), which we’ll study in detail in Chapter 8. But, it is possible to have an alias for data types similar to what we have for packages. For example, to create an alias for an integer type you can do:

type IZ int

Now to declare an integer variable, we have to use an alias like:

var a IZ = 5

If you have more than one type to define, you can use the factored keyword form, as in:

type (
  IZ int
  FZ float32
  STR string
)

In the above code, we create IZ, FZ, STR as an alias for int, float32, and string respectively.

Conversions

Sometimes a value needs to be converted into a value of another type called type-casting. Go does not allow implicit conversion, which means Go never does such a conversion by itself. The conversion must be done explicitly as valueOfTypeB = typeB(valueOfTypeA). How about writing a program on type-casting and observing the result? Let’s get started.

• Line 5: We declare a floating-point variable called number, and print the value in the next line.
• Line 7: We print the type-casted value by converting the value to int type using int(number). You can see that the value 5.2 becomes 5 after type-casting.