The right way of mapping 0, j, k, ^, $ to g0, gj, gk, g^, g$ when wrap is set

Question

First, I'm not sure just mapping j to gj always is a good idea, because, for instance, I don't want j to behave as gj when wrap is off and the line is longer than the screen.

How can I make 0, j, k, ^, $ behave like g0, gj, gk, g^, g$ when wrap is set? What is the proper way to do so?

I thought a good starting point could be

function! s:setDisplayLinesMovementWhenWrapOn()
  if &wrap
    nnoremap <buffer> j gj
    nnoremap <buffer> k gk
    nnoremap <buffer> 0 g0
    nnoremap <buffer> ^ g^
    nnoremap <buffer> $ g$
  else
    nunmap <buffer> j
    nunmap <buffer> k
    nunmap <buffer> 0
    nunmap <buffer> ^
    nunmap <buffer> $
  endif
endfunction

augroup DisplayLinesMovementWhenWrapOn
  autocmd!
  autocmd OptionSet wrap call s:setDisplayLinesMovementWhenWrapOn()
augroup END

But probably I also need another autocmd to call s:setDisplayLinesMovementWhenWrapOn when a buffer is read? Or a file? Or what?

Answer 1

You can use expression mappings for cases like this; normally a Vim mapping just sends the keys on the right-hand-side of a :map command straight to Vim, but with expression mappings it's interpreted as a VimScript expression, and the resulting value is used. You can use this to check if wrap is set.

nnoremap <expr> j &wrap ? 'gj' : 'j'

As far as I know and as I read the docs, gj (and related) already behave identical to j when wrapping is off, so I'm not sure if this is a very useful mapping as such, but this is the general strategy to make mappings behave different depending on which settings you have enabled/disabled.

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Bonus tip: you can also use :execute to create mappings, since all of these are so similar. For example:

for k in 'jk0^$'
    exe printf("nnoremap <expr> %s &wrap ? 'g%s' : '%s'", k, k, k)
endfor