Go concepts

Go is a statically typed language#

Meaning that a variable type must be known at compile time. When a variable is defined, a type is assigned to it. This type cannot be changed later in the program. In a given scope, only one variable can exist with a given name of a given type. Other statically typed languages: Java, C#.

Opposed to the statically typed, there are dynamically typed languages: Python, Ruby, JavaScript. In a dynamically typed language, it is possible to define a variable and assign a value of one type to it and then immidiately after that assign a value of a different type to that same variable.

var name = 123
name = "smth"

Short assignment#

Inside a function, when declaring a variable and assigning a value to it, a short assignment statement n := 3 can be used instead of var n int = 3 containing var keyword and the variable type int. Outside a function, the var keyword must always be used when declaring a variable.

Go documentation

GOPATH environment variable#

GOPATH environment variable contains a colon separated string with a list of paths to search Go code in. It is used to import the listed in Go applications dependency packages.

GOPATH girectory has three child directories: src, bin, pkg.

When using modules, GOPATH is no longer used for resolving imports. However, it is still used to store downloaded source code (in GOPATH/pkg/mod) and compiled commands (in GOPATH/bin).

More details on GOPATH: Go documentation

Go package types#

There are two package types in Go:

• executable, the package named main. A binary is created after building this package. Package main must contain a function called main,
• library, the packages with names other that main. Binaries are not created after building these packages. Go program execution always starts from main function.

Array vs Slice#

An Array is a fixed length sequence of elements of a given type, while a Slice is a variable length array.

uintptr vs unsafe.Pointer#

uintptr is an integer type. It is an integer representation of a memory address. But it is not a live reference to memory blocks it is pointing to. usafe.Pointer is a pointer type. It is a pointer to an arbitrary type. stackoverflow unsafe package documentation

rune type#

Is an alias of int32, it represents a Unicode code point. Go documentation

Generate random number#

Given some int n, generate a random number within it. In order to do this:

• get a seed as a unique int64 number from the current Unix timestamp,
• create a Source of randomness based on the obtained seed,
• create a Rand object based on the Source of randomness,
• get a random number from range starting from 0 to the given n using the Rand.Intn function.

source := rand.NewSource(time.Now().UnixNano())
r := rand.New(source)
randomNumber := r.Intn(n)