The region in the program where a variable is known is called the scope of that variable. Until now, we have only seen how to create top-level or global variables that are accessible from anywhere in the program. By contrast, variables defined in a local scope can only be used within that scope. A common example of a local scope is the code inside a function. Using global scope variables is not advisable for several reasons, notably the performance. If the value and type can change at any moment in the program, the compiler cannot optimize the code.

So, restricting the scope of a variable to local scope is better. This can be done by defining them within a function or a control construct, as we will see in the following chapters. This way, we can use the same variable name more than once without name conflicts.

Let's take a look at the following code fragment:

# code in chapter 2\scope.jl
x = 1.0 # x is Float64
x = 1 # now x is Int
# y::Float64 = 1.0 # LoadError: "y is not...