# Module `std::string` The string module defines the String type which represents UTF8 encoded strings. - [Struct `String`](#std_string_String) - [Constants](#@Constants_0) - [Function `utf8`](#std_string_utf8) - [Function `from_ascii`](#std_string_from_ascii) - [Function `to_ascii`](#std_string_to_ascii) - [Function `try_utf8`](#std_string_try_utf8) - [Function `as_bytes`](#std_string_as_bytes) - [Function `into_bytes`](#std_string_into_bytes) - [Function `is_empty`](#std_string_is_empty) - [Function `length`](#std_string_length) - [Function `append`](#std_string_append) - [Function `append_utf8`](#std_string_append_utf8) - [Function `insert`](#std_string_insert) - [Function `substring`](#std_string_substring) - [Function `index_of`](#std_string_index_of) - [Function `internal_check_utf8`](#std_string_internal_check_utf8) - [Function `internal_is_char_boundary`](#std_string_internal_is_char_boundary) - [Function `internal_sub_string`](#std_string_internal_sub_string) - [Function `internal_index_of`](#std_string_internal_index_of) - [Function `bytes`](#std_string_bytes) - [Function `sub_string`](#std_string_sub_string)

use std::ascii;
use std::option;
use std::vector;

## Struct `String` A String holds a sequence of bytes which is guaranteed to be in utf8 format.

public struct String has copy, drop, store

Fields

bytes: vector<u8>

## Constants An invalid UTF8 encoding.

const EInvalidUTF8: u64 = 1;

Index out of range.

const EInvalidIndex: u64 = 2;

## Function `utf8` Creates a new string from a sequence of bytes. Aborts if the bytes do not represent valid utf8.

public fun utf8(bytes: vector<u8>): std::string::String

Implementation

public fun utf8(bytes: vector<u8>): String {
    assert!(internal_check_utf8(&bytes), EInvalidUTF8);
    String { bytes }
}

## Function `from_ascii` Convert an ASCII string to a UTF8 string

public fun from_ascii(s: std::ascii::String): std::string::String

Implementation

public fun from_ascii(s: ascii::String): String {
    String { bytes: s.into_bytes() }
}

## Function `to_ascii` Convert an UTF8 string to an ASCII string. Aborts if s is not valid ASCII

public fun to_ascii(s: std::string::String): std::ascii::String

Implementation

public fun to_ascii(s: String): ascii::String {
    let String { bytes } = s;
    bytes.to_ascii_string()
}

## Function `try_utf8` Tries to create a new string from a sequence of bytes.

public fun try_utf8(bytes: vector<u8>): std::option::Option<std::string::String>

Implementation

public fun try_utf8(bytes: vector<u8>): Option<String> {
    if (internal_check_utf8(&bytes)) option::some(String { bytes })
    else option::none()
}

## Function `as_bytes` Returns a reference to the underlying byte vector.

public fun as_bytes(s: &std::string::String): &vector<u8>

Implementation

public fun as_bytes(s: &String): &vector<u8> {
    &s.bytes
}

## Function `into_bytes` Unpack the string to get its underlying bytes.

public fun into_bytes(s: std::string::String): vector<u8>

Implementation

public fun into_bytes(s: String): vector<u8> {
    let String { bytes } = s;
    bytes
}

## Function `is_empty` Checks whether this string is empty.

public fun is_empty(s: &std::string::String): bool

Implementation

public fun is_empty(s: &String): bool {
    s.bytes.is_empty()
}

## Function `length` Returns the length of this string, in bytes.

public fun length(s: &std::string::String): u64

Implementation

public fun length(s: &String): u64 {
    s.bytes.length()
}

## Function `append` Appends a string.

public fun append(s: &mut std::string::String, r: std::string::String)

Implementation

public fun append(s: &mut String, r: String) {
    s.bytes.append(r.bytes)
}

## Function `append_utf8` Appends bytes which must be in valid utf8 format.

public fun append_utf8(s: &mut std::string::String, bytes: vector<u8>)

Implementation

public fun append_utf8(s: &mut String, bytes: vector<u8>) {
    s.append(utf8(bytes))
}

## Function `insert` Insert the other string at the byte index in given string. The index must be at a valid utf8 char boundary.

public fun insert(s: &mut std::string::String, at: u64, o: std::string::String)

Implementation

public fun insert(s: &mut String, at: u64, o: String) {
    let bytes = &s.bytes;
    assert!(at <= bytes.length() && internal_is_char_boundary(bytes, at), EInvalidIndex);
    let l = s.length();
    let mut front = s.substring(0, at);
    let end = s.substring(at, l);
    front.append(o);
    front.append(end);
    *s = front;
}

## Function `substring` Returns a sub-string using the given byte indices, where i is the first byte position and j is the start of the first byte not included (or the length of the string). The indices must be at valid utf8 char boundaries, guaranteeing that the result is valid utf8.

public fun substring(s: &std::string::String, i: u64, j: u64): std::string::String

Implementation

public fun substring(s: &String, i: u64, j: u64): String {
    let bytes = &s.bytes;
    let l = bytes.length();
    assert!(
        j <= l &&
            i <= j &&
            internal_is_char_boundary(bytes, i) &&
            internal_is_char_boundary(bytes, j),
        EInvalidIndex,
    );
    String { bytes: internal_sub_string(bytes, i, j) }
}

## Function `index_of` Computes the index of the first occurrence of a string. Returns s.length() if no occurrence found.

public fun index_of(s: &std::string::String, r: &std::string::String): u64

Implementation

public fun index_of(s: &String, r: &String): u64 {
    internal_index_of(&s.bytes, &r.bytes)
}

## Function `internal_check_utf8`

fun internal_check_utf8(v: &vector<u8>): bool

Implementation

native fun internal_check_utf8(v: &vector<u8>): bool;

## Function `internal_is_char_boundary`

fun internal_is_char_boundary(v: &vector<u8>, i: u64): bool

Implementation

native fun internal_is_char_boundary(v: &vector<u8>, i: u64): bool;

## Function `internal_sub_string`

fun internal_sub_string(v: &vector<u8>, i: u64, j: u64): vector<u8>

Implementation

native fun internal_sub_string(v: &vector<u8>, i: u64, j: u64): vector<u8>;

## Function `internal_index_of`

fun internal_index_of(v: &vector<u8>, r: &vector<u8>): u64

Implementation

native fun internal_index_of(v: &vector<u8>, r: &vector<u8>): u64;

## Function `bytes`

public fun bytes(s: &std::string::String): &vector<u8>

Implementation

public fun bytes(s: &String): &vector<u8> { s.as_bytes() }

## Function `sub_string`

public fun sub_string(s: &std::string::String, i: u64, j: u64): std::string::String

Implementation

public fun sub_string(s: &String, i: u64, j: u64): String {
    s.substring(i, j)
}