Before starting to write Go applications like a wizard, we should start with the very basic ingredients. You just can't craft an airplane when you don't know what a wing is! So in this chapter we're going to learn the very basic syntax idioms to get our feet wet.
This is a tradition. And we do respect some traditions [1]. The very first program
one should write when learning a programming language is a small one that
outputs the sentence: Hello World.
Ready? Go!
package main
import "fmt"
func main() {
fmt.Printf("Hello, world; καλημ ́ρα κóσμ or こんにちは世界\n")
}Output:
A Go program is constructed as a "package", which may in turn use facilities from other packages.
The statement package <something> (in our example: <something> is main)
tells which package this file is part of.
In order to print on screen the text "Hello, world..." we use a function called
Printf that comes from the fmt package that we imported using the
statement import "fmt" on the 3rd line.
Note
Every standalone Go program contains a package called main and its main function, after initialization, is where execution starts. The main.main function takes no arguments and returns no value.
This is actually the same idea as in perl packages and python modules. And as you may see, the big advantage here is: modularity and reusability.
By modularity, I mean that you can divide your program into several pieces each one answering a specific need. And by reusability, I mean that packages that you write, or that already are brought to your by Go itself, can be used many times without rewriting the functionalities they provide each and every time you need them.
For now, you can just think of packages from the perspective of their rasion d'être and advantages. Later we will see how to create our own packages.
On line 5, we declare our main function with the keyword func and its body
is enclosed between { and } just like in C, C++, Java and other
languages.
Notice that our main() function takes no arguments. But we will see when we
will study functions, that in Go, they can take arguments, and return no, or one,
or many values!
So on line 6, we called the function Printf that is defined in the fmt
packages that we imported in line 3.
The dot notation is what is used in Go to refer to data, or functions
located in imported packages. Again, this is not a Go's invention, since this
technique is used in several other languages such as Python:
<module_name>.<data_or_function>
Notice that the string we printed using Printf contains non-ASCII
characters (greek and japanese). In fact, Go, natively supports UTF-8 for string
and identifiers.
Go uses packages (like python's modules) to organize code. The function
main.main (function main located the in main package) is the entry-point of
every standalone Go program. Go uses UTF-8 for strings and identifiers and is
not limited to the old ASCII character set.
| [1] | It is said that the first "hello, world" program was written by Brian Kernighan in his tutorial "Programming in C: A Tutorial" at Bell Labs in 1974. And there is a "hello, world" example in the seminal book "The C programming Language" much often refered to as "K&R" by Brian Kernighan and Dennis Ritchie. |