How found offset index a string in rune using go - string

Question

How found offset index a string in []rune using go?
I can do this work with string type.
if i := strings.Index(input[offset:], "}}"); i > 0 {print(i);}
but i need for runes.
i have a rune and want get offset index.
how can do this work with runes type in go?
example for more undrestand want need:
int offset=0//mean start from 0 (this is important for me)
string text="123456783}}56"
if i := strings.Index(text[offset:], "}}"); i > 0 {print(i);}
output of this example is : 9
but i want do this with []rune type(text variable)
may?
see my current code : https://play.golang.org/p/seImKzVpdh
tank you.

Answer 1

Edit #2: You again indicated a new type "meaning" of your question: you want to search a string in a []rune.
Answer: this is not supported directly in the standard library. But it's easy to implement it with 2 for loops:
func search(text []rune, what string) int {
whatRunes := []rune(what)
for i := range text {
found := true
for j := range whatRunes {
if text[i+j] != whatRunes[j] {
found = false
break
}
}
if found {
return i
}
}
return -1
}
Testing it:
value := []rune("123}456}}789")
result := search(value, "}}")
fmt.Println(result)
Output (try it on the Go Playground):
7
Edit: You updated the question indicating that you want to search runes in a string.
You may easily convert a []rune to a string using a simple type conversion:
toSearchRunes := []rune{'}', '}'}
toSearch := string(toSearchRunes)
And from there on, you can use strings.Index() as you did in your example:
if i := strings.Index(text[offset:], toSearch); i > 0 {
print(i)
}
Try it on the Go Playground.
Original answer follows:
string values in Go are stored as UTF-8 encoded bytes. strings.Index() returns you the byte position if the given substring is found.
So basically what you want is to convert this byte-position to rune-position. The unicode/utf8 package contains utility functions for telling the rune-count or rune-length of a string: utf8.RuneCountInString().
So basically you just need to pass the substring to this function:
offset := 0
text := "123456789}}56"
if i := strings.Index(text[offset:], "}}"); i > 0 {
fmt.Println("byte-pos:", i, "rune-pos:", utf8.RuneCountInString(text[offset:i]))
}
text = "世界}}世界"
if i := strings.Index(text[offset:], "}}"); i > 0 {
fmt.Println("byte-pos:", i, "rune-pos:", utf8.RuneCountInString(text[offset:i]))
}
Output (try it on the Go Playground):
byte-pos: 9 rune-pos: 9
byte-pos: 6 rune-pos: 2
Note: offset must also be a byte position, because when slicing a string like text[offset:], the index is interpreted as byte-index.
If you want to get the index of a rune, use strings.IndexRune() instead of strings.Index().