How to edit a register in normal mode from a script

Question

I want to be able to write my own custom escape method.

If I want to paste the contents of register s while in insert mode, I can type <C-R>s<CR>.

If I want to escape all occurrences of \, I can type <C-R>=escape(@s, '\').

How do I paste the contents of register s while executing an arbitrary formatting function?

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Extra information:

The end goal is to be able to hit a key and append a function declaration from a .c file to a register. void MyClass::foo() { will turn into void foo();

I plan to solve this by writing an =escape-esque function that deletes words starting with capital letters, and does the equivalent of :substitute/ *{$/;/

Answer 1

If you can define it all in one substitute all then replace the escape, since that can be any function. <C-R>=substitute(@s, '\m\(\w\+\) \w\+::\([^{]\+\) {', '\1 \2;', '')<CR>

If you don't want to do it all in one substitute, or to give it a descriptive name, you can write your own function.

For example:

function! FunctionDeclaration(snip)
  return substitute(a:snip, '\m\(\w\+\) \w\+::\([^{]\+\) {', '\1 \2;', '')
endfunction

Then invoke it with <C-R>=FunctionDeclaration(@s)<CR>

See :help user-functions for defining your own function like FunctionDeclaration above.

See :help substitute() for how to perform a regex substitution against a variable.

The breakdown of the regex suggested above:

• \m - Enable magic so that the regex behavior is not impacted by user settings. See :help magic.
• \(\w\+\) - Match a series of one or more "word characters". Matches the void in the example. See :help \w. Capture the result of that part of the match into the first match group. See :help pattern-overview. This can be referenced with \1 in the replacement.
• \w\+:: - Match a series of one or more "word characters" followed by ::. This matches the MyClass:: in the example. This is not matched in a subgroup so it will be dropped in the replacement.
• \([^{]+\) - Match a series of characters which are not { in a subgroup. This matches the foo() in the example. Can be reference by \2 in the replacement.
• { - Match the literal { at the end. Not matched in a subgroup so it is dropped.