Convert between rune array/slice and string

• Convert string to runes
• Convert runes to string
• Performance

Convert string to runes

• When you convert a string to a rune slice, you get a new slice that contains the Unicode code points (runes) of the string.
• For an invalid UTF-8 sequence, the rune value will be 0xFFFD for each invalid byte.

r := []rune("ABC€")
fmt.Println(r)        // [65 66 67 8364]
fmt.Printf("%U\n", r) // [U+0041 U+0042 U+0043 U+20AC]

You can also use a range loop to access the code points of a string.

Convert runes to string

• When you convert a slice of runes to a string, you get a new string that is the concatenation of the runes converted to UTF-8 encoded strings.

• Values outside the range of valid Unicode code points are converted to \uFFFD, the Unicode replacement character �.

s := string([]rune{'\u0041', '\u0042', '\u0043', '\u20AC', -1})
fmt.Println(s) // ABC€�

Performance

These conversions create a new slice or string, and therefore have time complexity proportional to the number of bytes that are processed.

More efficient alternative

In some cases, you might be able to use a string builder, which can concatenate strings without redundant copying:

Efficient string concatenation [full guide]

Further reading

40+ practical string tips [cheat sheet]

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