Go Beginners' Essentials

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Go Beginners’ Essentials by Palash Kanti Kundu is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

Introduction

In this short guide, I will provide short handy notes for go language essentials. This is meant for Go Beginners but experienced programmers. So, any one coming from C, Java, C#, Python, Javascript background, can quickly catch up. I will also link the exercise files present in the same repository for easy reference.

This will be a collection of brief notes, just enough to get you started using Go. Taking your skills beyond the basics is completely your choice. Please do not treat this as complete language reference.

Pre-requisites

A Computer :)
Go compiler. Head to http://golang.org and download go for your OS. Steps are mentioned in the website.
Any Text Editor of your choice.
Prior experience with programming language like C, C++, Java, C#, Python. As the following notes will draw lots of analogy between the languages.

Introduction to Go

Go is a modern language which solves problems of some of the current programming languages. Companies like Google, Amazon are trying to leverage its out of box concurrency handling. Projects like Docker and Kubernetes are being written in Go.

In my opinion Go is -

C/C++ without the noisy pointer arithmatic
Java/C# without try, catch
Java/C# without overloading
Java/C# without inheritance
C/C++ with built-in concurrency handling
C/C++ with garbage collection
Java/C# without the need of a Virtual Machine

Some unique features of Go are -

Unused variable/package detection during compile time itself, resulting in optimal executable file genration and optimal memory usage
Extreme level of type checking during compilation, eliminating the need of bugs caused by typecasting during runtime.
You do not need public or private keyword still make your variables or methods public or private
A built-in formatting tool to avoid the Formatting Problems in a multi developer system.

Basics

Exercise File: 1.go

Similar Commenting Styles from C, C++, Java
Semi-colon are not mandatory.
Has concept of packages like java and you have to import necessary packages to run the program
You must need a main package definition for running on console
You must need a main function definition for running on console
go run runs the file
go build creates an executable based on the platform you are running
Strings are automatically UTF. You do not need special packages to support multi-lingual system.
go fmt command formats the source code as per its own standards thus solving the problem of a multi-developer development system where each developer follows their own formatting styles.
Go built application has an associated application run time. No Virtual Machine is required to run the application.
Go has some of the Object Oriented Features - Interfaces, Custom Types, Structs, Methods
Go does not have these Object Oriented Features - Inheritance, Polymorphism, Method or Operator overloading, implicit numeric conversion, Exception Handling

Variable Declaration

Exercise Files: 2.1.go, 2.2.go, 2.3.go, 2.4.go

Variable declaration is a mix of javascript var and C/Java type declaration - var x int
Go has many integer definitions - int8, int16, int32, int64, int. The int type defaults to 32 bit or 64 bit based on platform. So, be careful if you have specific use case. Oherwise, you may go out of space or may get errors supporting your desired values.
Go also supports unsigned integer definitions like - uint8, uint16, uint32, uint64 and uint. Automatic size definition goes for uint as well.
Go has an alias for uint8 and that is byte
Floats are either float32 or float64. No automatic definition for floats.
Default value for number type variables are 0 or 0
If your program consists of any unused variable, the program will not even compile. So, get rid of memory issues in the compile time itself. Imagine, you have declared an array of int64 of size 86400 * 64 and left it unused, essentially you are wasting almost 42 MB of main memory. Go, gets rid of that during compile time itself.
Go, even raises compiler error for unused but assigned variables
Like unused variables, go raises compilation error for unused imports too
However, go does not raise error for a blank function.
You can get around the compilation error of unused variable by throwing away the value. You can name thhe variable as _ to throw away its value

Strong type check system

Exercise Files: 3.1.go, 3.2.go, 3.3.go, 3.4.go, 3.5.go

Go has a very strong type check system in place
Go does not allow you to assign integer variables to float variables
Operation between an integer and a float is not allowed
Operation between an integer and an unsigned integer is not allowed
Operation between float32 and float64 is also not allowed
Division between two integers results an integer
To get the float result, declare all associated variables as floats
Like python you can leave the type inference on compiler. You can use := operator for that
You can assign multiple variables on a single line using ,

Branching

Exercise Files: 4.1.go (Requires an integer console argument), 4.2.go

Usage: go run 4.1.go 7 go run 4.2.go 1

Supports if else ladder, however like python you do not need parenthesis to be wrapped around the condition
Conditional statements can have &&and ||
If conditions have an optional assignment statement
Also supports switch and like Java, C# it supports string variables in the condition
You do not need break statement in switch
Multiple cases can be comma separated
default is optional
switch can work without a condition, which is an alternative to if/else
switch also can have optional assignment
The starting parenthesis must be placed on the same line as of the if/switch statement

Looping

Exercise File: 5.go, fizzbuzz.go

go has only for loop
for can be used as while and while true loop as well
You can use break and continue within loop

Basic Understanding of Strings

Exercise File: 6.go

String is an immutable byte (uint8) array in go
In the built in package, you get some string handling operations like, we get strlen() in C
Go string slices can be taken based on array indexes, syntax is like list slices in python
Like Java, C# strings in go can be concatenated
As already mentioned earlier, strings are by default unicode in go
Multi line strings can be created using backticks
In the fmt package, we also get a funtion Sprintf. This function returns a string instead of displaying on console.

Basic Understanding of Slices

Exercise File: 7.go

A slice is a wrapper over actual array in go
The declaration of array and slice are similar except you remove the length in definition of slice while array is fixed length
Like ArrayList in Java, slice is graowable. For all practical purposes, I would like to think slice as ArrayList in Java or List in C# or List in python. Though the concept is not exactly the same, they work similar.
len function can be used over slices, the indexing and taking out a slice from an array or another slice is pretty similar as of python or as discussed in the basic understanding of strings
All elements of the same slice must be of same type
You can use for loop to iterate over a slice
You can use range keyword for iteration
You can use range with two variables that gives both values and indexes

Map

Exercise File: 8.go

map in go is same as Map<T, T> in java or Dictionary<T, T> in dotnet or dict in python
You declare a map using map keyword
While initializing map, you need the trailing comma and that’s a must
You can get value of a key similar like python or C#
One catch of go map, if you want to query for a key that does not exist in the map, it returns the default value for the type of the value.
To check if the key exists in a map, you need double context return
len function returns the number of keys present in map
Upserting a value in map is similar of python
To delete a value from map use builtin delete function
Iteration of map can be done using for loop with range either in single or in double context form

Functions

Exercise File: 9.go

You define functions in go similar to C functions or Java functions, only the return type or variable types are declared post the variable or function definition.

e.g. func add(a int, b int) int this code defines an add function with two integer parameters and integer return type

In go, you can return more than one variable, you use parenthesis to group the return type

e.g. func divide(dividend int, divisor int) (int, int, error) declares divide function which can return three output. error is a special type in go. I would like to think as Exception in Java.

You can return multiple values simply as comma separated

e.g. return dividend / divisor, dividend % divisor, nil. nil is Go is comparable with null in Java/C#

Error returning is heavily utilised in go and we already used error earlier in this series to check the presence of error in the return. Well, this is something like, checking HTTP Status Code before dealing with the response.
Calling a function is exactly the same as calling a function in C/Javascript
If a function returns more than one value, we have to use those many variables to assign the returns.

e.g. quotient, remainder, error := divide(5,0). You can also discard values that you won’t use by simply using _ to get rid of unused variable error (quotient, _, _ = divide(10,3) will discard the remainder and the error)

Pointers

Exercise Files: 10.1.go, 10.2.go

Like Java, primitive types are passed by value, even primitive arrays and strings. Remember string is an array of uint
All other values are passed by reference including slices

Destructors

Exercise File: 11.go

The __del__() in python or finalize() in Java can be compared to defer keywords in go
Go autoamatically cleans up the memory using garbage collector but for other resources like file, network, you can use the defer
defer statements are executed in reverse
defer statements will run regardless of if the code ran successfully or threw error

Structs

Exercise File: 12.go

Like C, you can define your own struct, this works similar as a class in Java or C#. The definition can be done using type and struct keywords.
You need to create the instance of the struct to be used in your code
You can create an instance of struct simply like C# but without the new keyword
If you leave any attribute empty while creating the struct, they will get default value according to the type
The assigning of values in struct is similar like assigning values in map
While prining the value, it only prints the values stored in the attrbutes
To see the struct like json you can use the +v in printf
struct can have one or more method associated with it
Defining method on struct is similar to that of defining function except you have to mention on which struct the method works upon
Like functions, methods too can be either pass by value or pass by reference. Pass by reference is more common
To define a method that is pass by value, we use the syntax - func (p Product) Value() float64 where p is the name of the variable Product is the defined struct and Value is the name of the method. Opening and closing braces define it has a method. This kind of methods do not change the value of the struct attributes.
To define a method that is pass by reference, we use the syntax - func (p *Product) SellProduct(). Notice the asterix before the struct type. This type of method can change the value of the struct attributes. The asteric defines that the method works on the pointer of the struct
Invoking method on struct is similar to that of invoking methods on Java or C#.
You can write a constructor function in go and it behaves like a constructor in Java or C#