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---
# SPDX-FileCopyrightText: 2022 Laurent Modolo
#
# SPDX-License-Identifier: AGPL-3.0-or-later
title: "Formation Go"
author: "Laurent Modolo"
date: "2022/11/08"
output:
beamer_presentation:
df_print: tibble
fig_caption: no
highlight: tango
latex_engine: xelatex
slide_level: 1
theme: metropolis
ioslides_presentation:
highlight: tango
slidy_presentation:
highlight: tango
classoption: aspectratio=169
---
```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = FALSE)
```
# Formation Go:
- ARAMIS
- Sebastien Binet
- Monday 26 September - Tuesday 27 September 2022 All Day
- https://tour.golang.org
\begin{center}
\href{https://github.com/sbinet/margo}{https://github.com/sbinet/margo}
\end{center}
# What is Go?
Go is a new, general-purpose programming language.
- Compiled
- Statically typed
- Concurrent
- Simple
- Productive
History:
- Project starts at Google in 2007 (by Griesemer, Pike, Thompson)
- Open source release in November 2009
# Install Go
[https://go.dev/doc/install](https://go.dev/doc/install)
```sh
mkdir -p $HOME/go
export GOPATH=$HOME/go
export PATH=$GOPATH/bin:$PATH
````
everything is in the `go` folder
# Install and run a go programm
```
go install -v github.com/sbinet/margo/cmd/margo-hello@latest
```
go install downloaded (cloned, in git speak) the whole `github.com/sbinet/margo` repository (under `$GOPATH/pkg/mod`) and compiled the `margo-hello` command. As the compilation was successful, it also installed the `margo-hello` command under `$GOPATH/bin`.
# The `go` tool
Compile and run code
```sh
go run hello.go
```
Test code
```sh
go test archive/zip
ok archive/zip 19.557s
```
Build the files in the current directory:
```sh
go build
```
Fetch and install the `websocket` package (in the current module):
```sh
go get golang.org/x/net/websocket
```
# Workspace
```
go
├── bin
│ ├── margo
│ ├── margo-hello
│ ├── motion
│ ├── ...
│ ├── revive
│ └── staticcheck
├── pkg
│ ├── mod
│ └── sumdb
└── src
└── github.com
```
- `bin` executable binaries
- `pkg` compiled object files
- `src` source code
# `pkg`
```sh
go install -v github.com/sbinet/margo/cmd/margo-hello@latest
```
- `go/pkg/mod/github.com/sbinet/margo@v0.0.0-20220927190215-3215db22d608`
- `go/bin/margo-hello`
# `src`
```sh
mkdir -p $GOPATH/src/gitbio.ens-lyon.fr/margo
cd $GOPATH/src/gitbio.ens-lyon.fr/margo
go mod init
go: creating new go.mod: module gitbio.ens-lyon.fr/margo # create a go.mod file
```
```
mkdir -p $GOPATH/src/gitbio.ens-lyon.fr/margo/hello
cp $GOPATH/pkg/mod/github.com/sbinet/margo@v0.0.0-20220927190215-3215db22d608/cmd/margo-hello/main.go $GOPATH/src/gitbio.ens-lyon.fr/margo/hello/
```
```
go install gitbio.ens-lyon.fr/margo/hello
hello
Hello MarGo!
```
# Langage
- primitive types
```go
int, uint, uint8, ..., uint64, int8, ... int64
bool, string
float32, float64
complex64, complex128
```
- structs
```go
struct {
Name string
Year int
}
```
# Langage
- arrays and slices
```go
[3]string, []float64
```
- maps
```go
map[string]int
```
- pointers
```go
*int, *Person
```
# Declaration
Normal declaration:
```go
var text string = "hello"
```
You can omit types:
```go
var text = "hello"
```
```go
text := "hello" //create and init
```
This code won't compile:
```
var freezing Fahrenheit = 32
var boiling Celsius = 100
sauna := (freezing + boiling) / 2
```
There's no implicit numeric conversion in Go.
# Functions
A sum function:
```go
func sum(a int, b int) int {
return a + b
}
```
A function with multiple return values:
Made clearer by naming the return values:
```go
func divMod(a, b int) (quo, rem int) {
return a / b, a % b
}
```
# Pointers
Go has pointers:
```go
var p *int
p = new(int)
```
But no pointer arithmetics:
```go
var p *int = &a[0]
var q = p+2 // invalid
```
There's `new` but there's no `delete`.
Memory is garbaged collected after it's no longer accessible.
# Memory allocation
The compiler decides where to allocate based on escape analysis.
Using `new` doesn't imply using the heap:
`stack.go`:
```go
func get() int {
n := new(int)
return *n
}
````
And not all values in the heap are created with `new`:
`heap.go`:
```go
func get() *int {
n := 4
return &n
}
```
# Packages & Imports
Every [[https://golang.org/][Go]] program is made up of packages.
Programs start running in `package` `main`.
This program is using the packages with import paths `"fmt"` and `"math/rand"`.
By convention, the package name is the same as the last element of the import path.
For instance, the `"math/rand"` package comprises files that begin with the statement `package` `rand`.
```
package main
import (
"fmt"
"math/rand"
)
func main() {
fmt.Println("My favorite number is", rand.Intn(10))
}
```
# Exported names
In [[https://golang.org/][Go]], a name is *exported* if it begins with a *capital* *letter*.
For example, `Pizza` is an exported name, as is `Pi`, which is exported from the `math` package.
`pizza` and `pi` do not start with a capital letter, so they are not exported.
When importing a package, you can refer only to its exported names.
Any "unexported" names are not accessible from outside the package.
Run the code. Notice the error message.
# Documentation
Browsing documentation is performed with `go` `doc`.
```sh
go doc os | less
PACKAGE DOCUMENTATION
package os
import "os"
Package os provides a platform-independent interface to operating system
functionality. The design is Unix-like, although the error handling is
Go-like; failing calls return values of type error rather than error
numbers. Often, more information is available within the error. For
example, if a call that takes a file name fails, such as Open or Stat,
the error will include the failing file name when printed and will be of
type *PathError, which may be unpacked for more information.
```
# Documentation
Browsing documentation is performed with `go` `doc`.
```sh
go doc os File | less
type File struct {
// contains filtered or unexported fields
}
File represents an open file descriptor.
func Create(name string) (file *File, err error)
Create creates the named file mode 0666 (before umask), truncating it if
it already exists. If successful, methods on the returned File can be
used for I/O; the associated file descriptor has mode O_RDWR. If there
is an error, it will be of type *PathError.
func Open(name string) (file *File, err error)
Open opens the named file for reading. If successful, methods on the
returned file can be used for reading; the associated file descriptor
has mode O_RDONLY. If there is an error, it will be of type *PathError.
```
# Goroutines
What is a goroutine? It's an independently executing function, launched by a go statement.
It has its own call stack, which grows and shrinks as required.
It's very cheap. It's practical to have thousands, even hundreds of thousands of goroutines.
It's not a thread.
There might be only one thread in a program with thousands of goroutines.
Instead, goroutines are multiplexed dynamically onto threads as needed to keep all the goroutines running.
But if you think of it as a very cheap thread, you won't be far off
# Goroutines
```go
func main() {
boring("boring!")
}
func boring(msg string) {
for i := 0; ; i++ {
fmt.Println(msg, i)
time.Sleep(time.Second)
}
}
```
# Channels
A channel in Go provides a connection between two goroutines, allowing them to communicate.
```go
func main() {
c := make(chan string)
go boring("boring!", c)
for i := 0; i < 5; i++ {
fmt.Printf("You say: %q\n", <-c) // Receive expression is just a value.
}
}
```
# Channels
A channel in Go provides a connection between two goroutines, allowing them to communicate.
```go
func boring(msg string, c chan string) {
for i := 0; ; i++ {
c <- fmt.Sprintf("%s %d", msg, i) // Expression to be sent can be any suitable value.
time.Sleep(time.Duration(rand.Intn(1e3)) * time.Millisecond)
}
}
```
# For scientific development
https://github.com/gonum
\begin{center}
\href{https://doc.rust-lang.org/book/}{https://doc.rust-lang.org/book/}
\end{center}