Tip #102: smart mapping for tab completion

I'm used to complete words with <tab>, however when editing source I can't just map that to vim keyword completion because I sometime need to insert real tabs,
since it mostly happen when at the beginning of the line or after a ; and before a one line comma (java, c++ or perl anyone...) I've come to find the following really usefull
This is how you can map the <tab> key in insert mode while still being able to use it when at the start of a line or when the preceding char is not a keyword character.
in a script file in a plugin directory or in your .vimrc file:
first define a function which returns a <tab> or a <C-N> depending on the context:

function InsertTabWrapper()
      let col = col('.') - 1
      if !col || getline('.')[col - 1] !~ '\k'
          return "\<tab>"
      else
          return "\<c-p>"
      endif
endfunction

then define the appropriate mapping:
inoremap <tab> <c-r>=InsertTabWrapper()<cr>

the trick here is the use of the <c-r>= in insert mode to be able to call your function without leaving insert mode.
:help i_CTRL-R
Benoit

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