Return the union of two character sets.
Synopsis
Description
This function returns a new character set which contains all of the characters
in cs0
as well as all of the characters
in cs
.
Example
This creates a character set which includes all letters and numbers
constexpr lut_chars alpha_chars(
"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
"abcdefghijklmnopqrstuvwxyz");
constexpr lut_chars alnum_chars = alpha_chars + "0123456789";
Complexity
Constant.