add stringx.FirstN with ellipsis (#916)

core/stringx/strings.go

@@ -41,12 +41,16 @@ func Filter(s string, filter func(r rune) bool) string {
 }
 
 // FirstN returns first n runes from s.
-func FirstN(s string, n int) string {
+func FirstN(s string, n int, ellipsis ...string) string {
 	var i int
 
 	for j := range s {
 		if i == n {
-			return s[:j]
+			ret := s[:j]
+			for _, each := range ellipsis {
+				ret += each
+			}
+			return ret
 		}
 		i++
 	}

core/stringx/strings_test.go

@@ -94,10 +94,11 @@ func TestFilter(t *testing.T) {
 
 func TestFirstN(t *testing.T) {
 	tests := []struct {
-		name   string
-		input  string
-		n      int
-		expect string
+		name     string
+		input    string
+		n        int
+		ellipsis string
+		expect   string
 	}{
 		{
 			name:   "english string",
@@ -105,6 +106,13 @@ func TestFirstN(t *testing.T) {
 			n:      8,
 			expect: "anything",
 		},
+		{
+			name:     "english string with ellipsis",
+			input:    "anything that we use",
+			n:        8,
+			ellipsis: "...",
+			expect:   "anything...",
+		},
 		{
 			name:   "english string more",
 			input:  "anything that we use",
@@ -117,6 +125,13 @@ func TestFirstN(t *testing.T) {
 			n:      2,
 			expect: "我是",
 		},
+		{
+			name:     "chinese string with ellipsis",
+			input:    "我是中国人",
+			n:        2,
+			ellipsis: "...",
+			expect:   "我是...",
+		},
 		{
 			name:   "chinese string",
 			input:  "我是中国人",
@@ -127,7 +142,7 @@ func TestFirstN(t *testing.T) {
 
 	for _, test := range tests {
 		t.Run(test.name, func(t *testing.T) {
-			assert.Equal(t, test.expect, FirstN(test.input, test.n))
+			assert.Equal(t, test.expect, FirstN(test.input, test.n, test.ellipsis))
 		})
 	}
 }