Braces don't match with regex equals operator

Question

function! s:foo()
    normal! yiw
    if @" =~# '\vf[0-9]b\('
        echom 'Matches!'
    endif
endfunction

nnoremap <silent> * :<c-u>call <sid>foo()<cr>

" f2b⣿(

When my cursor position is ⣿ and I press *, why doesn't it say 'Matches!'. I just can't get any braces to match (<, (, [, or {).

I would also be very happy about any recommended references, as I h regex or h =~ isn't really helpful, as it just covers the basics...

Answer 1

For the w, motion, see :h word:

                                                        word
A word consists of a sequence of letters, digits and underscores, or a
sequence of other non-blank characters, separated with white space (spaces,
tabs, <EOL>).  This can be changed with the 'iskeyword' option.  An empty line
is also considered to be a word.
                                                        WORD
A WORD consists of a sequence of non-blank characters, separated with white
space.  An empty line is also considered to be a WORD.

So, you probably need to set iskeyword, or use W.

However, depending on what your actual use for this thing is, you don't need to copy the text. Use <cword> (or <cWORD>):

    <cword>    is replaced with the word under the cursor (like star)
    <cWORD>    is replaced with the WORD under the cursor (see WORD)

So:

function! s:foo()
    let l:word = expand('<cWORD>')
    if l:word =~# '\vf[0-9]b\('
        echom 'Matches!'
    endif
endfunction