Initial commit - learning the basics

This commit is contained in:
V 2025-08-30 13:55:18 +01:00
commit 194ca9b7a9
27 changed files with 830 additions and 0 deletions

33
api_gin/go.mod Normal file
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module learning.local/api_gin
go 1.24.5
require (
github.com/bytedance/sonic v1.13.3 // indirect
github.com/bytedance/sonic/loader v0.3.0 // indirect
github.com/cloudwego/base64x v0.1.5 // indirect
github.com/cloudwego/iasm v0.2.0 // indirect
github.com/gabriel-vasile/mimetype v1.4.9 // indirect
github.com/gin-contrib/sse v1.1.0 // indirect
github.com/gin-gonic/gin v1.10.1 // indirect
github.com/go-playground/locales v0.14.1 // indirect
github.com/go-playground/universal-translator v0.18.1 // indirect
github.com/go-playground/validator/v10 v10.27.0 // indirect
github.com/goccy/go-json v0.10.5 // indirect
github.com/json-iterator/go v1.1.12 // indirect
github.com/klauspost/cpuid/v2 v2.3.0 // indirect
github.com/leodido/go-urn v1.4.0 // indirect
github.com/mattn/go-isatty v0.0.20 // indirect
github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd // indirect
github.com/modern-go/reflect2 v1.0.2 // indirect
github.com/pelletier/go-toml/v2 v2.2.4 // indirect
github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
github.com/ugorji/go/codec v1.3.0 // indirect
golang.org/x/arch v0.19.0 // indirect
golang.org/x/crypto v0.40.0 // indirect
golang.org/x/net v0.42.0 // indirect
golang.org/x/sys v0.34.0 // indirect
golang.org/x/text v0.27.0 // indirect
google.golang.org/protobuf v1.36.6 // indirect
gopkg.in/yaml.v3 v3.0.1 // indirect
)

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github.com/bytedance/sonic v1.13.3 h1:MS8gmaH16Gtirygw7jV91pDCN33NyMrPbN7qiYhEsF0=
github.com/bytedance/sonic v1.13.3/go.mod h1:o68xyaF9u2gvVBuGHPlUVCy+ZfmNNO5ETf1+KgkJhz4=
github.com/bytedance/sonic/loader v0.1.1/go.mod h1:ncP89zfokxS5LZrJxl5z0UJcsk4M4yY2JpfqGeCtNLU=
github.com/bytedance/sonic/loader v0.3.0 h1:dskwH8edlzNMctoruo8FPTJDF3vLtDT0sXZwvZJyqeA=
github.com/bytedance/sonic/loader v0.3.0/go.mod h1:N8A3vUdtUebEY2/VQC0MyhYeKUFosQU6FxH2JmUe6VI=
github.com/cloudwego/base64x v0.1.5 h1:XPciSp1xaq2VCSt6lF0phncD4koWyULpl5bUxbfCyP4=
github.com/cloudwego/base64x v0.1.5/go.mod h1:0zlkT4Wn5C6NdauXdJRhSKRlJvmclQ1hhJgA0rcu/8w=
github.com/cloudwego/iasm v0.2.0 h1:1KNIy1I1H9hNNFEEH3DVnI4UujN+1zjpuk6gwHLTssg=
github.com/cloudwego/iasm v0.2.0/go.mod h1:8rXZaNYT2n95jn+zTI1sDr+IgcD2GVs0nlbbQPiEFhY=
github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/gabriel-vasile/mimetype v1.4.9 h1:5k+WDwEsD9eTLL8Tz3L0VnmVh9QxGjRmjBvAG7U/oYY=
github.com/gabriel-vasile/mimetype v1.4.9/go.mod h1:WnSQhFKJuBlRyLiKohA/2DtIlPFAbguNaG7QCHcyGok=
github.com/gin-contrib/sse v1.1.0 h1:n0w2GMuUpWDVp7qSpvze6fAu9iRxJY4Hmj6AmBOU05w=
github.com/gin-contrib/sse v1.1.0/go.mod h1:hxRZ5gVpWMT7Z0B0gSNYqqsSCNIJMjzvm6fqCz9vjwM=
github.com/gin-gonic/gin v1.10.1 h1:T0ujvqyCSqRopADpgPgiTT63DUQVSfojyME59Ei63pQ=
github.com/gin-gonic/gin v1.10.1/go.mod h1:4PMNQiOhvDRa013RKVbsiNwoyezlm2rm0uX/T7kzp5Y=
github.com/go-playground/locales v0.14.1 h1:EWaQ/wswjilfKLTECiXz7Rh+3BjFhfDFKv/oXslEjJA=
github.com/go-playground/locales v0.14.1/go.mod h1:hxrqLVvrK65+Rwrd5Fc6F2O76J/NuW9t0sjnWqG1slY=
github.com/go-playground/universal-translator v0.18.1 h1:Bcnm0ZwsGyWbCzImXv+pAJnYK9S473LQFuzCbDbfSFY=
github.com/go-playground/universal-translator v0.18.1/go.mod h1:xekY+UJKNuX9WP91TpwSH2VMlDf28Uj24BCp08ZFTUY=
github.com/go-playground/validator/v10 v10.27.0 h1:w8+XrWVMhGkxOaaowyKH35gFydVHOvC0/uWoy2Fzwn4=
github.com/go-playground/validator/v10 v10.27.0/go.mod h1:I5QpIEbmr8On7W0TktmJAumgzX4CA1XNl4ZmDuVHKKo=
github.com/goccy/go-json v0.10.5 h1:Fq85nIqj+gXn/S5ahsiTlK3TmC85qgirsdTP/+DeaC4=
github.com/goccy/go-json v0.10.5/go.mod h1:oq7eo15ShAhp70Anwd5lgX2pLfOS3QCiwU/PULtXL6M=
github.com/google/gofuzz v1.0.0/go.mod h1:dBl0BpW6vV/+mYPU4Po3pmUjxk6FQPldtuIdl/M65Eg=
github.com/json-iterator/go v1.1.12 h1:PV8peI4a0ysnczrg+LtxykD8LfKY9ML6u2jnxaEnrnM=
github.com/json-iterator/go v1.1.12/go.mod h1:e30LSqwooZae/UwlEbR2852Gd8hjQvJoHmT4TnhNGBo=
github.com/klauspost/cpuid/v2 v2.0.9/go.mod h1:FInQzS24/EEf25PyTYn52gqo7WaD8xa0213Md/qVLRg=
github.com/klauspost/cpuid/v2 v2.3.0 h1:S4CRMLnYUhGeDFDqkGriYKdfoFlDnMtqTiI/sFzhA9Y=
github.com/klauspost/cpuid/v2 v2.3.0/go.mod h1:hqwkgyIinND0mEev00jJYCxPNVRVXFQeu1XKlok6oO0=
github.com/knz/go-libedit v1.10.1/go.mod h1:MZTVkCWyz0oBc7JOWP3wNAzd002ZbM/5hgShxwh4x8M=
github.com/leodido/go-urn v1.4.0 h1:WT9HwE9SGECu3lg4d/dIA+jxlljEa1/ffXKmRjqdmIQ=
github.com/leodido/go-urn v1.4.0/go.mod h1:bvxc+MVxLKB4z00jd1z+Dvzr47oO32F/QSNjSBOlFxI=
github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
github.com/modern-go/concurrent v0.0.0-20180228061459-e0a39a4cb421/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd h1:TRLaZ9cD/w8PVh93nsPXa1VrQ6jlwL5oN8l14QlcNfg=
github.com/modern-go/concurrent v0.0.0-20180306012644-bacd9c7ef1dd/go.mod h1:6dJC0mAP4ikYIbvyc7fijjWJddQyLn8Ig3JB5CqoB9Q=
github.com/modern-go/reflect2 v1.0.2 h1:xBagoLtFs94CBntxluKeaWgTMpvLxC4ur3nMaC9Gz0M=
github.com/modern-go/reflect2 v1.0.2/go.mod h1:yWuevngMOJpCy52FWWMvUC8ws7m/LJsjYzDa0/r8luk=
github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0t5Ec4=
github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
github.com/stretchr/objx v0.4.0/go.mod h1:YvHI0jy2hoMjB+UWwv71VJQ9isScKT/TqJzVSSt89Yw=
github.com/stretchr/objx v0.5.0/go.mod h1:Yh+to48EsGEfYuaHDzXPcE3xhTkx73EhmCGUpEOglKo=
github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
github.com/stretchr/testify v1.7.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
github.com/stretchr/testify v1.8.0/go.mod h1:yNjHg4UonilssWZ8iaSj1OCr/vHnekPRkoO+kdMU+MU=
github.com/stretchr/testify v1.8.1/go.mod h1:w2LPCIKwWwSfY2zedu0+kehJoqGctiVI29o6fzry7u4=
github.com/twitchyliquid64/golang-asm v0.15.1 h1:SU5vSMR7hnwNxj24w34ZyCi/FmDZTkS4MhqMhdFk5YI=
github.com/twitchyliquid64/golang-asm v0.15.1/go.mod h1:a1lVb/DtPvCB8fslRZhAngC2+aY1QWCk3Cedj/Gdt08=
github.com/ugorji/go/codec v1.3.0 h1:Qd2W2sQawAfG8XSvzwhBeoGq71zXOC/Q1E9y/wUcsUA=
github.com/ugorji/go/codec v1.3.0/go.mod h1:pRBVtBSKl77K30Bv8R2P+cLSGaTtex6fsA2Wjqmfxj4=
golang.org/x/arch v0.19.0 h1:LmbDQUodHThXE+htjrnmVD73M//D9GTH6wFZjyDkjyU=
golang.org/x/arch v0.19.0/go.mod h1:bdwinDaKcfZUGpH09BB7ZmOfhalA8lQdzl62l8gGWsk=
golang.org/x/crypto v0.40.0 h1:r4x+VvoG5Fm+eJcxMaY8CQM7Lb0l1lsmjGBQ6s8BfKM=
golang.org/x/crypto v0.40.0/go.mod h1:Qr1vMER5WyS2dfPHAlsOj01wgLbsyWtFn/aY+5+ZdxY=
golang.org/x/net v0.42.0 h1:jzkYrhi3YQWD6MLBJcsklgQsoAcw89EcZbJw8Z614hs=
golang.org/x/net v0.42.0/go.mod h1:FF1RA5d3u7nAYA4z2TkclSCKh68eSXtiFwcWQpPXdt8=
golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
golang.org/x/sys v0.34.0 h1:H5Y5sJ2L2JRdyv7ROF1he/lPdvFsd0mJHFw2ThKHxLA=
golang.org/x/sys v0.34.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
golang.org/x/text v0.27.0 h1:4fGWRpyh641NLlecmyl4LOe6yDdfaYNrGb2zdfo4JV4=
golang.org/x/text v0.27.0/go.mod h1:1D28KMCvyooCX9hBiosv5Tz/+YLxj0j7XhWjpSUF7CU=
google.golang.org/protobuf v1.36.6 h1:z1NpPI8ku2WgiWnf+t9wTPsn6eP1L7ksHUlkfLvd9xY=
google.golang.org/protobuf v1.36.6/go.mod h1:jduwjTPXsFjZGTmRluh+L6NjiWu7pchiJ2/5YcXBHnY=
gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=
nullprogram.com/x/optparse v1.0.0/go.mod h1:KdyPE+Igbe0jQUrVfMqDMeJQIJZEuyV7pjYmp6pbG50=
rsc.io/pdf v0.1.1/go.mod h1:n8OzWcQ6Sp37PL01nO98y4iUCRdTGarVfzxY20ICaU4=

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package main
import (
"github.com/gin-gonic/gin"
"net/http"
"fmt"
"encoding/json"
)
func main() {
router := gin.Default()
router.GET("/", func(c *gin.Context) {
c.JSON(http.StatusOK, gin.H{
"message": "Hiya!",
})
})
router.GET("/ping", func(c *gin.Context) {
c.JSON(http.StatusOK, gin.H{
"message": "pong",
})
})
router.GET("/pokemon/:name", func(c *gin.Context) {
name := c.Param("name")
url := fmt.Sprintf("https://pokeapi.co/api/v2/pokemon/%s", name)
res, err := http.Get(url)
if err != nil {
fmt.Printf("Could not retrieve info for Pokemon %s!", name)
}
var result map[string]any
decoder := json.NewDecoder(res.Body)
defer res.Body.Close()
if err := decoder.Decode(&result); err != nil {
fmt.Printf("Could not read response body!")
}
c.JSON(http.StatusOK, gin.H{
"message": "success",
"pokemon_info": result,
})
})
router.Run()
}

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module learning.local/hello
go 1.24.5
replace learning.local/using_modules => ../using_modules
require learning.local/using_modules v0.0.0-00010101000000-000000000000

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package main
import (
"fmt"
"log"
"learning.local/using_modules"
)
func main () {
// Set properties of the predefined Logger, including
// the log entry prefix and a flag to disable printing
// the time, source fiile, and line number.
log.SetPrefix("using_modules: ")
log.SetFlags(0)
// A slice of names
names := []string{"Gladys", "Yoda", "Darth Vader"}
// Request greeting messages for the names
messages, err := using_modules.Hellos(names)
if err != nil {
log.Fatal(err)
}
// If no error was returned, print the returned map of
// messages to the console
fmt.Println(messages)
}

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package using_modules
import (
"fmt"
"errors"
"math/rand"
)
// Hello returns a greeting for the named person
func Hello(name string) (string, error) {
// If no name was given, return an error with a message
if name == "" {
return "", errors.New("Empty name!")
}
message := fmt.Sprintf(randomFormat(), name)
return message, nil
}
// randomFormat returns one of a set of greeting messages. The returned
// message is selected at random.
func randomFormat() string {
// A slice of message formats
formats := []string{
"Hi, %v. Welcome!",
"Great to see you, %v",
"Hail, %v! Well met!",
}
// Return a randomly selected message format by specifying
// a random index for the slice of formats.
return formats[rand.Intn(len(formats))]
}

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module learning/tour
go 1.24.5
require rsc.io/quote v1.5.2
require (
golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c // indirect
rsc.io/sampler v1.3.0 // indirect
)

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golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c h1:qgOY6WgZOaTkIIMiVjBQcw93ERBE4m30iBm00nkL0i8=
golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
rsc.io/quote v1.5.2 h1:w5fcysjrx7yqtD/aO+QwRjYZOKnaM9Uh2b40tElTs3Y=
rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPXsUe+TKr0=
rsc.io/sampler v1.3.0 h1:7uVkIFmeBqHfdjD+gZwtXXI+RODJ2Wc4O7MPEh/QiW4=
rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=

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package main
import "fmt"
import "rsc.io/quote"
func main() {
fmt.Println("Hello Go!")
fmt.Println(quote.Go())
}

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package main
import (
"fmt"
"math/cmplx"
)
var c, java, python bool
var n, m int = 1, 2
var (
ToBe bool = false
MaxInt uint64 = 1<<64 - 1
z complex128 = cmplx.Sqrt(-5 + 12i)
)
func add(x, y int) int {
return x + y
}
func swap (x, y string) (string, string) {
return y, x
}
func split(sum int) (x, y int) {
x = sum * 4 / 9
y = sum - x
return
}
func main() {
fmt.Println(add(42,13))
x := [3]int{2,1,1}
fmt.Println(x)
a, b := swap("hello", "go")
fmt.Println(a, b)
fmt.Println(split(17))
var i int
fmt.Println(i, c, python, java)
c, java, python := true, true, "no!"
k := 3
fmt.Println(k, n, m, c, python, java)
fmt.Printf("Type: %T Value: %v\n", ToBe, ToBe)
fmt.Printf("Type: %T Value: %v\n", MaxInt, MaxInt)
fmt.Printf("Type: %T Value: %v\n", z, z)
g := 42
f := float64(g)
u := uint(f)
fmt.Println(g, f, u)
const Pi = 3.14
const World = "世界"
const Truth = true
fmt.Println("Hello", World)
fmt.Println("Happy", Pi, "Day")
fmt.Println("Go rules?", Truth)
}

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package main
import (
"fmt"
"math/rand"
"math"
)
func main() {
fmt.Println("My favorite number is", rand.Intn(10))
fmt.Println(math.Pi)
}

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package main
import (
"fmt"
)
func Sqrt(x float64) float64 {
}
func main() {
fmt.Println(Sqrt(2))
}

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package main
import (
"fmt"
"math"
)
func pow(x, n, lim float64) float64 {
if v := math.Pow(x, n); v < lim {
return v
} else {
fmt.Printf("%g >= %g\n", v, lim)
}
return lim
}
func main() {
fmt.Println(
pow(3, 2, 10),
pow(3, 3, 20),
)
}

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package main
import (
"fmt"
)
func Sqrt(x float64) float64 {
precision := 0.00001
old_z := 0.0
z := x
iter := 0
for (z - old_z) > precision {
iter += 1
old_z := z
z -= (z*z - x) / (2*z)
if old_z - z < 0 {
if ((old_z - z) * -1) < precision {
fmt.Println("Required precision has been reached after", iter, "iterations! Square root of", x , "is", z)
return z
}
} else if (old_z - z) < precision {
fmt.Println("Required precision has been reached after", iter, "iterations! Square root of", x , "is", z)
return z
}
}
return z
}
func main() {
fmt.Println(Sqrt(2))
fmt.Println(Sqrt(29))
}

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package main
import (
"fmt"
"math"
)
func sqrt(x float64) string {
if x < 0 {
return sqrt(-x) + "i"
}
return fmt.Sprint(math.Sqrt(x))
}
func main() {
sum := 0
for i := 0; i < 10; i++ {
sum += 1
}
fmt.Println(sum)
sum_2 := 1
for sum_2 < 1000 {
sum_2 += sum_2
}
fmt.Println(sum_2)
fmt.Println(sqrt(2), sqrt(-4))
}

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package main
import (
"fmt"
"time"
"runtime"
)
func letsDefer(text string) {
defer fmt.Println(text)
fmt.Print("I have deferred: ")
}
func main() {
fmt.Print("Go runs on ")
switch os := runtime.GOOS; os {
case "darwin":
fmt.Println("macOS.")
case "linux":
fmt.Println("Linux.")
default:
fmt.Printf("%s.\n", os)
}
fmt.Println("When's Saturday?")
today := time.Now().Weekday()
switch time.Saturday {
case today + 0:
fmt.Println("Today.")
case today + 1:
fmt.Println("Tomorrow.")
case today + 2:
fmt.Println("In two days.")
default:
fmt.Println("Too far away.")
}
t := time.Now()
switch {
case t.Hour() < 12:
fmt.Println("Good morning!")
case t.Hour() < 17:
fmt.Println("Good afternoon")
default:
fmt.Println("Good evening.")
}
letsDefer("Some stuff")
fmt.Println("Counting...")
for i:=0; i<10; i++ {
defer fmt.Println(i)
}
fmt.Println("Done!")
}

39
tour_of_go/l4/2 Normal file
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package main
import "fmt"
func main() {
var aa [2]string
aa[0] = "Hello"
aa[1] = "World"
fmt.Println(aa[0], aa[1])
fmt.Println(aa)
primes := [6]int{2, 3, 5, 7, 11, 13}
fmt.Println(primes)
var s []int = primes[1:4]
fmt.Printf("The primes are %d and the slice is %d", primes, s)
// Slices are references to array sections
// Changing elements in a slice results in changes to the array
// So other slices referencing the same array section will also be changed
names := [4]string{
"John",
"Paul",
"George",
"Ringo",
}
fmt.Println(names)
a := names[0:2]
b := names[1:3]
fmt.Println(a, b)
// Now make some changes
b[0] = "XXX"
fmt.Println(a, b)
fmt.Println(names)
}

23
tour_of_go/l4/append.go Normal file
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package main
import "fmt"
func printSlice(s []int) {
fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}
func main() {
var s []int
printSlice(s)
s = append(s, 0)
printSlice(s)
s = append(s, 1)
printSlice(s)
s = append(s, 2, 3, 4)
printSlice(s)
s = append(s, 56)
printSlice(s)
}

72
tour_of_go/l4/arrays.go Normal file
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package main
import "fmt"
func main() {
var aa [2]string
aa[0] = "Hello"
aa[1] = "World"
fmt.Println(aa[0], aa[1])
fmt.Println(aa)
primes := [6]int{2, 3, 5, 7, 11, 13}
fmt.Println(primes)
var s []int = primes[1:4]
fmt.Printf("The primes are %d and the slice is %d", primes, s)
// Slices are references to array sections
// Changing elements in a slice results in changes to the array
// So other slices referencing the same array section will also be changed
names := [4]string{
"John",
"Paul",
"George",
"Ringo",
}
fmt.Println(names)
a := names[0:2]
b := names[1:3]
fmt.Println(a, b)
// Now make some changes
b[0] = "XXX"
fmt.Println(a, b)
fmt.Println(names)
// Slice literals - like array literals, but without the length
q := []int{2, 3, 5, 7, 11, 13}
fmt.Println(q)
r := []bool{true, false, true, true, false, true}
fmt.Println(r)
sx := []struct {
i int
b bool
}{
{2, true},
{3, false},
{5, true},
{7, true},
{11, false},
{13, true},
}
fmt.Println(sx)
// Slice defaults
ss := []int{2, 3, 5, 7, 11, 13}
ss = ss[1: 4]
fmt.Println(ss)
ss = ss[:2]
fmt.Println(ss)
ss = ss[1:]
fmt.Println(ss)
}

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package main
import (
"fmt"
"strings"
)
func printSlice(s []int) {
fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}
func main() {
a := make([]int, 5)
printSlice(a)
b := make([]int, 0, 5)
printSlice(b)
c := b[:2]
printSlice(c)
d := c[2:5]
printSlice(d)
// Slices can contain any type including other slices
board := [][]string{
[]string{"_", "_", "_"},
[]string{"_", "_", "_"},
[]string{"_", "_", "_"},
}
board[0][0] = "X"
board[2][2] = "O"
board[1][2] = "X"
board[1][0] = "O"
board[0][2] = "X"
for i := 0; i < len(board); i++ {
fmt.Printf("%s\n", strings.Join(board[i], " "))
}
}

18
tour_of_go/l4/pointers.go Normal file
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package main
import "fmt"
func main() {
i, j := 42, 2701
p := &i
fmt.Println(*p)
*p = 21
fmt.Println(i)
p = &j
*p = *p / 37
fmt.Println(j)
fmt.Println(i, j)
}

21
tour_of_go/l4/range.go Normal file
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package main
import "fmt"
var pow = []int{1, 2, 4, 8, 16, 32, 64, 128}
func main() {
for i, v := range pow {
fmt.Printf("2**%d = %d\n", i, v)
}
// You can skip the index by assigning it to "_"
// Or you can skip the value by omitting the 2nd value -> "for i := range XXX"
new_pow := make([]int, 10)
for i := range new_pow {
new_pow[i] = 1 << uint(i)
}
for _, value := range new_pow {
fmt.Printf("%d\n", value)
}
}

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package main
import "fmt"
func printSlice(s []int) {
fmt.Printf("len=%d cap=%d %v\n", len(s), cap(s), s)
}
func main() {
s := []int{2, 3, 5, 7, 11, 13}
printSlice(s)
s = s[:0]
printSlice(s)
s = s[:4]
printSlice(s)
s = s[2:]
printSlice(s)
// Extend beyond capacity
// s = s[:10]
// printSlice(s)
// Zero value of a slice is nil
var ns []int
printSlice(ns)
if ns == nil {
fmt.Println("nil!!")
}
}

27
tour_of_go/l4/structs.go Normal file
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package main
import "fmt"
type Vertex struct {
X int
Y int
}
var (
v1 = Vertex{1, 2}
v2 = Vertex{X: 1}
v3 = Vertex{}
p = &Vertex{1, 2}
)
func main() {
v := Vertex{1, 2}
v.X = 4
fmt.Println(v)
o := &v
o.X = 12
fmt.Printf("New vertex value is %d\n", v)
fmt.Println(v1, p, v2, v3)
}

3
using_modules/go.mod Normal file
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module learning.local/using_modules
go 1.24.5

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package using_modules
import (
"fmt"
"errors"
"math/rand"
)
// Hello returns a greeting for the named person
func Hello(name string) (string, error) {
// If no name was given, return an error with a message
if name == "" {
return "", errors.New("empty name")
}
message := fmt.Sprintf(randomFormat(), name)
return message, nil
}
// Hellos retruns a map that associates each of the named people
// with a greeting message.
func Hellos(names []string) (map[string]string, error) {
// A map to associate names with messages
messages := make(map[string]string)
// Loop through the received slice of names, calling
// the Hello function to get a message for each name.
for _, name := range names {
message, err := Hello(name)
if err != nil {
return nil, err
}
// In the map, associate the terieved message with
// the name.
messages[name] = message
}
return messages, nil
}
// randomFormat returns one of a set of greeting messages. The returned
// message is selected at random.
func randomFormat() string {
// A slice of message formats
formats := []string{
"Hi, %v. Welcome!",
"Great to see you, %v!",
"Hail, %v! Well met!",
}
// Return a randomly selected message format by specifying
// a random index for the slice of formats.
return formats[rand.Intn(len(formats))]
}

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package using_modules
import (
"testing"
"regexp"
)
// TestHelloName calls greetings.Hello with a name, checking
// for a valid return value.
func TestHelloName(t *testing.T) {
name := "Gladys"
want := regexp.MustCompile(`\b`+name+`\b`)
msg, err := Hello("Gladys")
if !want.MatchString(msg) || err != nil {
t.Errorf(`Hello("Gladys") = %q, %v, want match for %#q, nill`, msg, err, want)
}
}
// TestHelloEmpty calls greeting.Hello with an empty string,
// checking for an error
func TestHelloEmpty(t *testing.T) {
msg, err := Hello("")
if msg != "" || err == nil {
t.Errorf(`Hello("") = %q, %v, want "", error`, msg, err)
}
}