CategoryReferences

Scope in Go

When we talk about scope in any programming language, we are referring to how the code can access variables. Scope defines where a variable can be accessed based on how it is declared. Scope in Go is fairly simplistic. In this post, we will be talking about scope in Go.

Go has three specific types of variables: local variables, global variables and formal parameters. First of all, local variables are found inside of a block or function. Also, global variables are found outside of all functions. Finally, formal parameters are the variables in function definitions.

scope

Local Variables

Local variables are the most common type in Go. They can only be used by the statements that are in the block of code in which they were made. This is to say that local variables are not accessible by functions outside of their own. Look at the example below.

These variables are bound to the main function. They can’t be accessed by a function or block of code outside of the main function.

Global Variables

Global variables are typically defined outside of all functions and at the top of the program. This style of defining a variable at the top is idiomatic in Go. Global variables have a lifetime that last as long as the program runs. They also can be accessed by any function in the program that follows their declaration.

In this program, both of the functions have access to our global variable. This has its advantages and disadvantages. Consequently, any function has access to this variable which means any function can change this variable.

scopeFormal Function Parameters

Finally, we have formal parameters. These variables are treated like local variables and they gain preference over global variables. Therefore, if the global variable shares the name of a formal function parameter the formal parameter will be used. So, Let us look at an example of this.

In this somewhat nonsensical program, we have three variables that share the name, g. One is a global variable, one is a local variable and the other is a formal parameter. We are also calling the references for these variables to show that they are different. This reference notation is something we will look at closer in our next post. For now, all you need to know is that the three values are different from one another. Furthermore, each time we print the reference to g out, we are calling a different block of memory. 

Conclusion

In this post, we looked at scope in Go. We looked at local variables, global variables and formal functional parameters in Go. We touched briefly on pointers and references in this post as well. In our next posts, we will be going over Pointers and References in Go. 

Manipulating Strings in Go

Strings are a pretty standard primitive type in most programming languages. They give the programmer the ability to output messages and store data. Today, we are going to look at strings and string manipulation in Go. We are also going to take a look at some of the print and input functions in Go.

Defining Strings in Go

Strings in Go are defined using double quotes "". You can’t use single quotes '' in Go because this is reserved for single characters or runes. A string by definition is a collection of characters surrounded by double quotes. In Go, we can do many cool things with strings such as regex, data storage, output, debugging, etc.

hello-world-go

You may have noticed that in our Hello world program from the last post we imported a library called fmt. The fmt library gives us access to I/O in Go. This library gives us access to different print functions as well as scanner functions. We can use these print functions to print out to our terminal/console. We can also use the scanner functions to take in input from the command line.

Using I/O for Input and Output

The program above allows us to take in an input and then output "Hello, Input!" to the screen. In the program, we are using two different print functions and a scanner function. We are also making use of a reference and a string variable.

The fmt.Println() function will print the string or arguments that are in the parenthesis out then automatically create a new line. We could also get this behavior by changing that function to fmt.Print("\n"). The \n character set is what is called a newline character. The backslash is the escape character and the “n” is what tells it to create a new line. The fmt.Scanln() function lets us scan the input until the user hits the enter key or creates a new line.

Formatting Strings in Go

The fmt.Printf() function stands for print format. It allows us to format the string inside of the function. You may have noticed the use of a %s pair of characters. This is telling the string that we want to format that area of the string by inputting the value of a string variable, in this case, input. There are many other two letter codes that we can use to format strings in Go.

strings-in-go

As you can see above, there are many different ways to format strings and the values being passed into those strings via the fmt.printf() function. All of the print functions in the fmt library are called variadic functions. Variadic functions in Go let the user input as many arguments into them as they want. We will talk about this more later but for now it is worth mentioning at least.

A Brief Word on References and Pointers

There is at least one more thing worth looking at from this piece of code which is the line: fmt.Scanln(&input). The reason this line is so important to look at is because we are using something called a reference in place of the normal variable input. In many low-level programming languages, we have something called a pointer and something else called a reference. The and & sign right before the input variable inside of the Scanln() function indicates that we are referencing the variable called input. The & operator finds the address of a variable and we assign the input to this variable. We will talk further about references when we get to pointers later down the line.

Conclusion

In this post, we looked at strings in Go. We also looked at how we can manipulate these strings and we looked at the basic I/O library in Go. We briefly talked about variadic functions, references and pointers as well. In our next posts, we will talk about logical operators, Loops and basic control flow in Go.