Skip to main content

Module 0x1::string

The string module defines the String type which represents UTF8 encoded strings.

use 0x1::ascii;
use 0x1::option;
use 0x1::vector;

Struct String​

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

struct String has copy, drop, store
Fields
bytes: vector<u8>

Constants​

Index out of range.

const EInvalidIndex: u64 = 2;

An invalid UTF8 encoding.

const EInvalidUTF8: u64 = 1;

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>): 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: ascii::String): 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: string::String): 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>): option::Option<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: &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: 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: &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: &string::String): u64
Implementation
public fun length(s: &String): u64 {
    s.bytes.length()
}

Function append​

Appends a string.

public fun append(s: &mut string::String, r: 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 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 string::String, at: u64, o: 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: &string::String, i: u64, j: u64): 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: &string::String, r: &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​

[DEPRECATED]

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

Function sub_string​

[DEPRECATED]

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