utf8-offset-5.3-5.4.d.ts

// https://www.lua.org/manual/5.3/manual.html#6.5

/**
 * This library provides basic support for UTF-8 encoding. It provides all its
 * functions inside the table utf8. This library does not provide any support
 * for Unicode other than the handling of the encoding. Any operation that needs
 * the meaning of a character, such as character classification, is outside its
 * scope.
 *
 * Unless stated otherwise, all functions that expect a byte position as a
 * parameter assume that the given position is either the start of a byte
 * sequence or one plus the length of the subject string. As in the string
 * library, negative indices count from the end of the string.
 */
declare namespace utf8 {
    /**
     * Returns the position (in bytes) where the encoding of the n-th character of
     * s (counting from position i) starts. A negative n gets characters before
     * position i. The default for i is 1 when n is non-negative and #s + 1
     * otherwise, so that utf8.offset(s, -n) gets the offset of the n-th character
     * from the end of the string. If the specified character is neither in the
     * subject nor right after its end, the function returns nil.
     *
     * As a special case, when n is 0 the function returns the start of the
     * encoding of the character that contains the i-th byte of s.
     *
     * This function assumes that s is a valid UTF-8 string.
     */
    function offset(s: string, n?: number, i?: number): number;
}