Replace fmt.Sprint with strconv.Itoa, specify slice capacity

Uber's Go style guide outlines a slight performance benefit when using
strconv over fmt:
dc025303c1/style.md (prefer-strconv-over-fmt)

Also specifiying slice capacity when it is known beforehand:
dc025303c1/style.md (specifying-slice-capacity)

Signed-off-by: Vartan Benohanian <vartanbeno@gmail.com>

reddit/emoji.go

@@ -11,6 +11,7 @@ import (
 	"net/http"
 	"net/url"
 	"os"
+	"strconv"
 	"strings"
 
 	"github.com/google/go-querystring/query"
@@ -63,6 +64,7 @@ func (e *emojis) UnmarshalJSON(data []byte) (err error) {
 		return
 	}
 
+	*e = make(emojis, 0, len(emojiMap))
 	for emojiName, emojiValue := range emojiMap {
 		emoji := new(Emoji)
 		err = json.Unmarshal(emojiValue, emoji)
@@ -120,8 +122,8 @@ func (s *EmojiService) SetSize(ctx context.Context, subreddit string, height, wi
 	path := fmt.Sprintf("api/v1/%s/emoji_custom_size", subreddit)
 
 	form := url.Values{}
-	form.Set("height", fmt.Sprint(height))
-	form.Set("width", fmt.Sprint(width))
+	form.Set("height", strconv.Itoa(height))
+	form.Set("width", strconv.Itoa(width))
 
 	req, err := s.client.NewRequest(http.MethodPost, path, form)
 	if err != nil {

reddit/gold.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"net/http"
 	"net/url"
+	"strconv"
 )
 
 // GoldService handles communication with the gold
@@ -37,7 +38,7 @@ func (s *GoldService) Give(ctx context.Context, username string, months int) (*R
 	path := fmt.Sprintf("api/v1/gold/give/%s", username)
 
 	form := url.Values{}
-	form.Set("months", fmt.Sprint(months))
+	form.Set("months", strconv.Itoa(months))
 
 	req, err := s.client.NewRequest(http.MethodPost, path, form)
 	if err != nil {

reddit/multi.go

@@ -58,8 +58,9 @@ func (n *SubredditNames) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
-	for _, sr := range subreddits {
-		*n = append(*n, sr.Name)
+	*n = make(SubredditNames, len(subreddits))
+	for i, sr := range subreddits {
+		(*n)[i] = sr.Name
 	}
 
 	return nil

reddit/post-and-comment.go

@@ -2,9 +2,9 @@ package reddit
 
 import (
 	"context"
-	"fmt"
 	"net/http"
 	"net/url"
+	"strconv"
 )
 
 // postAndCommentService handles communication with the post and comment
@@ -137,7 +137,7 @@ func (s *postAndCommentService) vote(ctx context.Context, id string, vote vote)
 
 	form := url.Values{}
 	form.Set("id", id)
-	form.Set("dir", fmt.Sprint(vote))
+	form.Set("dir", strconv.Itoa(int(vote)))
 	form.Set("rank", "10")
 
 	req, err := s.client.NewRequest(http.MethodPost, path, form)

reddit/post.go

@@ -339,7 +339,7 @@ func (s *PostService) PinToProfile(ctx context.Context, id string) (*Response, e
 	form.Set("id", id)
 	form.Set("state", "true")
 	form.Set("to_profile", "true")
-	// form.Set("num", fmt.Sprint(pos))
+	// form.Set("num", strconv.Itoa(pos))
 
 	req, err := s.client.NewRequest(http.MethodPost, path, form)
 	if err != nil {

reddit/things.go

@@ -398,6 +398,7 @@ func (l *trophyList) UnmarshalJSON(b []byte) error {
 		return err
 	}
 
+	*l = make(trophyList, 0, len(root.Trophies))
 	for _, thing := range root.Trophies {
 		if trophy, ok := thing.Trophy(); ok {
 			*l = append(*l, trophy)

reddit/widget.go

@@ -91,6 +91,7 @@ func (l *WidgetList) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
+	*l = make(WidgetList, 0, len(widgetMap))
 	for _, w := range widgetMap {
 		root := new(rootWidget)
 		err = json.Unmarshal(w, root)
@@ -301,6 +302,7 @@ func (l *WidgetLinkList) UnmarshalJSON(data []byte) error {
 		return err
 	}
 
+	*l = make(WidgetLinkList, 0, len(dataMap))
 	for _, d := range dataMap {
 		var widgetLinkDataMap map[string]json.RawMessage
 		err = json.Unmarshal(d, &widgetLinkDataMap)