Updated .gitignore to ignore .out and .test profiling files

Replaced interface{} with any in varfmt
Implemented varfmt, could be further optimized

.gitignore

@@ -3,3 +3,7 @@
 .vscode/
 
 /example/
+
+# Go profiling files
+*.out
+*.test

fetchall/main.go

@@ -10,50 +10,50 @@ import (
 	"time"
 )
 
-type HttpGetResult struct {
+type HTTPGetResult struct {
 	Success bool
 	Body    string
 	Elapsed time.Duration
 	Size    int
-	Url     string
+	URL     string
 	Error   error
 }
 
-func (result HttpGetResult) String() string {
+func (result HTTPGetResult) String() string {
 	if result.Success {
-		return fmt.Sprintf("%v\t%v\t%v", result.Elapsed, result.Size, result.Url)
+		return fmt.Sprintf("%v\t%v\t%v", result.Elapsed, result.Size, result.URL)
 	} else {
 		return result.Error.Error()
 	}
 }
 
-func GetHttpBody(url string, ch chan HttpGetResult) {
+func GetHTTPBody(url string, ch chan HTTPGetResult) {
 	startTime := time.Now()
 	resp, err := http.Get(url)
 	if err != nil {
-		ch <- HttpGetResult{Success: false, Error: err}
+		ch <- HTTPGetResult{Success: false, Error: err}
 		return
 	}
 	defer resp.Body.Close()
 	data, err := io.ReadAll(resp.Body)
 	if err != nil {
-		ch <- HttpGetResult{Success: false, Error: err}
+		ch <- HTTPGetResult{Success: false, Error: err}
 		return
 	}
-	ch <- HttpGetResult{
+	ch <- HTTPGetResult{
 		Success: true,
 		Body:    string(data),
 		Elapsed: time.Since(startTime),
 		Size:    len(data),
-		Url:     url,
+		URL:     url,
 	}
 }
 
 func main() {
 	startTime := time.Now()
-	urls, ch := os.Args[1:], make(chan HttpGetResult)
+	urls, ch := os.Args[1:], make(chan HTTPGetResult)
 	for _, url := range urls {
-		go GetHttpBody(url, ch)
+		go GetHTTPBody(url, ch)
 	}
 	for i := 0; i < len(urls); i++ {
 		fmt.Println(<-ch)

varfmt/fmt.go

@@ -2,6 +2,74 @@
 
 package varfmt
 
-func Sprintf(format string, args ...interface{}) string {
-	return ""
+import (
+	"fmt"
+	"strconv"
+	"strings"
+	"unicode/utf8"
+)
+
+// fmt.Sprintf does 1 alloc
+// this does 3-4 allocations and is a bit slower than fmt.Sprintf
+// can be further optimized, by casting args slice
+// to string without allocating new space (somehow)
+func Sprintf(format string, args ...any) string {
+	// init output strings.Builder and num rune buffer
+	// cant use strings.Builder for storing num since
+	// builder can't clear its contents without reallocating
+	output, num := strings.Builder{}, make([]rune, 0, 1)
+	// convert args slice to strArgs string slice
+	strArgs, maxLen := make([]string, len(args), cap(args)), 0
+	for i, arg := range args {
+		strArgs[i] = fmt.Sprint(arg)
+		if len(strArgs[i]) > maxLen {
+			maxLen = len(strArgs[i])
+		}
+	}
+	// allocate maximum possible length of the resulting string
+	output.Grow(len(format) + len(args)*maxLen)
+	start, argIndex := 0, 0
+	// decode runes one by one
+	for start < len(format) {
+		r, n := utf8.DecodeRuneInString(format[start:])
+		start += n
+		// if specifier is found, start forming index
+		if r == '{' {
+			numLength := 0
+			for {
+				r, n = utf8.DecodeRuneInString(format[start:])
+				start += n
+				if r == '}' {
+					break
+				}
+				numLength++
+				// append new rune if the number is bigger
+				// than the current buffer
+				if numLength >= len(num) {
+					num = append(num, r)
+				} else {
+					num[numLength] = r
+				}
+			}
+			var index int
+			// if specifier is empty get arg at argIndex
+			// otherwise get arg at the specified index from num
+			if len(num) == 0 {
+				index = argIndex
+			} else {
+				var err error
+				index, err = strconv.Atoi(string(num))
+				if err != nil {
+					panic(err)
+				}
+			}
+			output.WriteString(strArgs[index])
+			argIndex++
+			// set len of num to 0, but keep capacity
+			num = num[:0]
+			continue
+		}
+		output.WriteRune(r)
+	}
+	return output.String()
 }

varfmt/fmt_test.go

@@ -9,49 +9,49 @@ import (
 )
 
 func TestFormat(t *testing.T) {
-	s := make([]interface{}, 1002)
+	s := make([]any, 1002)
 	s[10] = 1
 	s[100] = 2
 	s[1000] = 3
 
 	for _, tc := range []struct {
 		format string
-		args   []interface{}
+		args   []any
 		result string
 	}{
 		{
 			format: "{}",
-			args:   []interface{}{0},
+			args:   []any{0},
 			result: "0",
 		},
 		{
 			format: "{0} {0}",
-			args:   []interface{}{1},
+			args:   []any{1},
 			result: "1 1",
 		},
 		{
 			format: "{1} {5}",
-			args:   []interface{}{0, 1, 2, 3, 4, 5, 6},
+			args:   []any{0, 1, 2, 3, 4, 5, 6},
 			result: "1 5",
 		},
 		{
 			format: "{} {} {} {} {}",
-			args:   []interface{}{0, 1, 2, 3, 4},
+			args:   []any{0, 1, 2, 3, 4},
 			result: "0 1 2 3 4",
 		},
 		{
 			format: "{} {0} {0} {0} {}",
-			args:   []interface{}{0, 1, 2, 3, 4},
+			args:   []any{0, 1, 2, 3, 4},
 			result: "0 0 0 0 4",
 		},
 		{
 			format: "Hello, {2}",
-			args:   []interface{}{0, 1, "World"},
+			args:   []any{0, 1, "World"},
 			result: "Hello, World",
 		},
 		{
 			format: "He{2}o",
-			args:   []interface{}{0, 1, "ll"},
+			args:   []any{0, 1, "ll"},
 			result: "Hello",
 		},
 		{
@@ -80,22 +80,22 @@ func BenchmarkFormat(b *testing.B) {
 	for _, tc := range []struct {
 		name   string
 		format string
-		args   []interface{}
+		args   []any
 	}{
 		{
 			name:   "small int",
 			format: "{}",
-			args:   []interface{}{42},
+			args:   []any{42},
 		},
 		{
 			name:   "small string",
 			format: "{} {}",
-			args:   []interface{}{"Hello", "World"},
+			args:   []any{"Hello", "World"},
 		},
 		{
 			name:   "big",
 			format: strings.Repeat("{0}{1}", 1000),
-			args:   []interface{}{42, 43},
+			args:   []any{42, 43},
 		},
 	} {
 		b.Run(tc.name, func(b *testing.B) {
@@ -111,21 +111,21 @@ func BenchmarkSprintf(b *testing.B) {
 	for _, tc := range []struct {
 		name   string
 		format string
-		args   []interface{}
+		args   []any
 	}{
 		{
 			name:   "small",
 			format: "%d",
-			args:   []interface{}{42},
+			args:   []any{42},
 		},
 		{
 			name:   "small string",
 			format: "%v %v",
-			args:   []interface{}{"Hello", "World"},
+			args:   []any{"Hello", "World"},
 		}, {
 			name:   "big",
 			format: strings.Repeat("%[0]v%[1]v", 1000),
-			args:   []interface{}{42, 43},
+			args:   []any{42, 43},
 		},
 	} {
 		b.Run(tc.name, func(b *testing.B) {