regex: ] in a character class

[Tobias Pankrath]

On Saturday, 12 December 2020 at 12:03:49 UTC, kdevel wrote:
> In some situations a ] must be escaped as in
>
>    auto re = regex(`^[a\]]$`); // match a and ] only
>
> Unfortunately dmd/phobos does not warn if you forget the 
> backslash:
>
>    auto re = regex(`^[a]]$`); // match a]
>
> This leads me to the documentation [1] which says
>
>    \c where c is one of [|*+?() 	Matches the character c itself.
>
> ] must be added to this list since \] obviously matches ]. 
> Additionally
> the statement
>
>    any character except [{|*+?()^$     Matches the character 
> itself.
>
> is not true since ] does not match itself when ] denotes the 
> end of
> a character class. I don't have a suggestion for better wording 
> yet.
>
> [1] https://dlang.org/phobos/std_regex.html

As I understand it, the statement is indeed true and a regex 
`]]]` would match and only match the string `]]]`. What should be 
added somewhere is

>   Inside character classes the character ']' has to be written 
> as '\]'.