reorganize: starting with funcs

25-functions/01-basics/bad.go

@@ -0,0 +1,26 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import "fmt"
+
+func showN() {
+	if N == 0 {
+		fmt.Println("showN       : N is zero, increment it.")
+		return
+	}
+	fmt.Printf("showN       : N = %d\n", N)
+}
+
+func incrN() {
+	N++
+}
+
+// you cannot declare a function within the same package with the same name
+// func incrN() {
+// }

25-functions/01-basics/main.go

@@ -0,0 +1,33 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+//
+// You need run this program like so:
+//   go run .
+//
+// This will magically pass all the go files in the current directory to the
+// Go compiler.
+//
+//
+// BUT NOT like so:
+//   go run main.go
+//
+// Because, the compiler needs to see global.go too
+// It can't magically find global.go — what you give is what you get.
+//
+
+package main
+
+// N is a shared counter which is BAD
+var N int
+
+func main() {
+	showN()
+	incrN()
+	incrN()
+	showN()
+}

25-functions/02-basics/main.go

@@ -0,0 +1,117 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+//
+// You need run this program like so:
+//   go run .
+//
+// This will magically pass all the go files in the current directory to the
+// Go compiler.
+//
+//
+// BUT NOT like so:
+//   go run main.go
+//
+// Because, the compiler needs to see global.go too
+// It can't magically find global.go — what you give is what you get.
+//
+
+package main
+
+import (
+	"fmt"
+	"strconv"
+)
+
+func main() {
+	local := 10
+	show(local)
+
+	incrWrong(local)
+	fmt.Printf("local → %d\n", local)
+
+	// incr(local)
+	local = incr(local)
+	show(local)
+
+	local = incrBy(local, 5)
+	show(local)
+
+	_, err := incrByStr(local, "TWO")
+	if err != nil {
+		fmt.Printf("err   → %s\n", err)
+	}
+
+	local, _ = incrByStr(local, "2")
+	show(local)
+
+	// CHAINING
+
+	// can't save the number back into main's local
+	show(incrBy(local, 2))
+	show(local)
+
+	// can't pass the results of the multiple-value returning func
+	// show(incrByStr(local, "3"))
+
+	// can call showErr directly because it accepts the same types
+	// of parameters as with incrByStr's result values.
+	// local = sanitize(incrByStr(local, "NOPE"))
+	// show(local)
+
+	local = sanitize(incrByStr(local, "2"))
+	show(local)
+
+	local = limit(incrBy(local, 5), 2000)
+	show(local)
+}
+
+func show(n int) {
+	// can't access main's local
+	// fmt.Printf("show : n = %d\n", local)
+	fmt.Printf("show  → n = %d\n", n)
+}
+
+// wrong: incr can't access to main's `local`
+func incrWrong(n int) {
+	// n := local
+	n++
+	// can't return (there are no result values)
+	// return n
+}
+
+func incr(n int) int {
+	n++
+	return n
+}
+
+func incrBy(n, factor int) int {
+	return n * factor
+}
+
+func incrByStr(n int, factor string) (int, error) {
+	m, err := strconv.Atoi(factor)
+	n = incrBy(n, m)
+	return n, err
+}
+
+func sanitize(n int, err error) int {
+	if err != nil {
+		return 0
+	}
+	return n
+}
+
+func limit(n, lim int) (m int) {
+	// var m int
+	m = n
+	if m >= lim {
+		m = lim
+	}
+	// return m
+	return
+}

25-functions/03-refactor-to-funcs/log.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org 4
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions/03-refactor-to-funcs/log_err_missing.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions/03-refactor-to-funcs/log_err_negative.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org -100
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions/03-refactor-to-funcs/log_err_str.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org FOUR
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions/03-refactor-to-funcs/main.go

@@ -0,0 +1,67 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+)
+
+func main() {
+	p := newParser()
+
+	// Scan the standard-in line by line
+	in := bufio.NewScanner(os.Stdin)
+	for in.Scan() {
+		p.lines++
+
+		parsed, err := parse(p, in.Text())
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+
+		domain, visits := parsed.domain, parsed.visits
+
+		// Collect the unique domains
+		if _, ok := p.sum[domain]; !ok {
+			p.domains = append(p.domains, domain)
+		}
+
+		// Keep track of total and per domain visits
+		p.total += visits
+
+		// create and assign a new copy of `visit`
+		p.sum[domain] = result{
+			domain: domain,
+			visits: visits + p.sum[domain].visits,
+		}
+	}
+
+	// Print the visits per domain
+	sort.Strings(p.domains)
+
+	fmt.Printf("%-30s %10s\n", "DOMAIN", "VISITS")
+	fmt.Println(strings.Repeat("-", 45))
+
+	for _, domain := range p.domains {
+		parsed := p.sum[domain]
+		fmt.Printf("%-30s %10d\n", domain, parsed.visits)
+	}
+
+	// Print the total visits for all domains
+	fmt.Printf("\n%-30s %10d\n", "TOTAL", p.total)
+
+	// Let's handle the error
+	if err := in.Err(); err != nil {
+		fmt.Println("> Err:", err)
+	}
+}

25-functions/03-refactor-to-funcs/parser.go

@@ -0,0 +1,53 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// result stores the parsed result for a domain
+type result struct {
+	domain string
+	visits int
+	// add more metrics if needed
+}
+
+// parser keep tracks of the parsing
+type parser struct {
+	sum     map[string]result // metrics per domain
+	domains []string          // unique domain names
+	total   int               // total visits for all domains
+	lines   int               // number of parsed lines (for the error messages)
+}
+
+// newParser constructs, initializes and returns a new parser
+func newParser() parser {
+	return parser{sum: make(map[string]result)}
+}
+
+// parse parses a log line and returns the parsed result with an error
+func parse(p parser, line string) (parsed result, err error) {
+	fields := strings.Fields(line)
+	if len(fields) != 2 {
+		err = fmt.Errorf("wrong input: %v (line #%d)", fields, p.lines)
+		return
+	}
+
+	parsed.domain = fields[0]
+
+	parsed.visits, err = strconv.Atoi(fields[1])
+	if parsed.visits < 0 || err != nil {
+		err = fmt.Errorf("wrong input: %q (line #%d)", fields[1], p.lines)
+		return
+	}
+
+	return
+}

25-functions/04-pass-by-value-semantics/log.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org 4
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions/04-pass-by-value-semantics/log_err_missing.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions/04-pass-by-value-semantics/log_err_negative.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org -100
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions/04-pass-by-value-semantics/log_err_str.txt

@@ -0,0 +1,6 @@
+learngoprogramming.com 10
+learngoprogramming.com 10
+golang.org FOUR
+golang.org 6
+blog.golang.org 20
+blog.golang.org 10

25-functions/04-pass-by-value-semantics/main.go

@@ -0,0 +1,53 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strings"
+)
+
+func main() {
+	p := newParser()
+
+	// Scan the standard-in line by line
+	in := bufio.NewScanner(os.Stdin)
+	for in.Scan() {
+		p.lines++
+
+		parsed, err := parse(p, in.Text())
+		if err != nil {
+			fmt.Println(err)
+			return
+		}
+
+		p = update(p, parsed)
+	}
+
+	// Print the visits per domain
+	sort.Strings(p.domains)
+
+	fmt.Printf("%-30s %10s\n", "DOMAIN", "VISITS")
+	fmt.Println(strings.Repeat("-", 45))
+
+	for _, domain := range p.domains {
+		parsed := p.sum[domain]
+		fmt.Printf("%-30s %10d\n", domain, parsed.visits)
+	}
+
+	// Print the total visits for all domains
+	fmt.Printf("\n%-30s %10d\n", "TOTAL", p.total)
+
+	// Let's handle the error
+	if err := in.Err(); err != nil {
+		fmt.Println("> Err:", err)
+	}
+}

25-functions/04-pass-by-value-semantics/parser.go

@@ -0,0 +1,74 @@
+// For more tutorials: https://blog.learngoprogramming.com
+//
+// Copyright © 2018 Inanc Gumus
+// Learn Go Programming Course
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+//
+
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"strings"
+)
+
+// result stores the parsed result for a domain
+type result struct {
+	domain string
+	visits int
+	// add more metrics if needed
+}
+
+// parser keep tracks of the parsing
+type parser struct {
+	sum     map[string]result // metrics per domain
+	domains []string          // unique domain names
+	total   int               // total visits for all domains
+	lines   int               // number of parsed lines (for the error messages)
+}
+
+// newParser constructs, initializes and returns a new parser
+func newParser() parser {
+	return parser{sum: make(map[string]result)}
+}
+
+// parse parses a log line and returns the parsed result with an error
+func parse(p parser, line string) (parsed result, err error) {
+	fields := strings.Fields(line)
+	if len(fields) != 2 {
+		err = fmt.Errorf("wrong input: %v (line #%d)", fields, p.lines)
+		return
+	}
+
+	parsed.domain = fields[0]
+
+	parsed.visits, err = strconv.Atoi(fields[1])
+	if parsed.visits < 0 || err != nil {
+		err = fmt.Errorf("wrong input: %q (line #%d)", fields[1], p.lines)
+		return
+	}
+
+	return
+}
+
+// update updates the parser for the given parsing result
+func update(p parser, parsed result) parser {
+	domain, visits := parsed.domain, parsed.visits
+
+	// Collect the unique domains
+	if _, ok := p.sum[domain]; !ok {
+		p.domains = append(p.domains, domain)
+	}
+
+	// Keep track of total and per domain visits
+	p.total += visits
+
+	// create and assign a new copy of `visit`
+	p.sum[domain] = result{
+		domain: domain,
+		visits: visits + p.sum[domain].visits,
+	}
+
+	return p
+}