introduce parts metadata.

autoload/airline/extensions/branch.vim

@@ -31,6 +31,6 @@ function! airline#extensions#branch#get_head()
 endfunction
 
 function! airline#extensions#branch#init(ext)
-  let g:airline_parts.branch = 'airline#extensions#branch#get_head'
+  call airline#parts#define_function('branch', 'airline#extensions#branch#get_head')
 endfunction
 

autoload/airline/extensions/bufferline.vim

@@ -14,5 +14,6 @@ function! airline#extensions#bufferline#init(ext)
     let g:bufferline_separator = ' '
   endif
 
-  let g:airline_parts.file = '%{bufferline#refresh_status()}'.bufferline#get_status_string()
+  call airline#parts#define_raw('file', '%{bufferline#refresh_status()}'.bufferline#get_status_string())
 endfunction
+

autoload/airline/extensions/hunks.vim

@@ -54,6 +54,6 @@ function! airline#extensions#hunks#get_hunks()
 endfunction
 
 function! airline#extensions#hunks#init(ext)
-  let g:airline_parts.hunks = 'airline#extensions#hunks#get_hunks'
+  call airline#parts#define_function('hunks', 'airline#extensions#hunks#get_hunks')
 endfunction
 

autoload/airline/parts.vim

@@ -1,14 +1,27 @@
 " MIT License. Copyright (c) 2013 Bailey Ling.
 " vim: et ts=2 sts=2 sw=2
 
-function! airline#parts#append(name)
-  let val = function(a:name)()
-  return empty(val) ? '' : '  '.g:airline_left_alt_sep.' '.val
+let s:parts = {}
+
+function! airline#parts#define(key, config)
+  let s:parts[a:key] = get(s:parts, a:key, {})
+  call extend(s:parts[a:key], a:config)
 endfunction
 
-function! airline#parts#prepend(name)
-  let val = function(a:name)()
-  return empty(val) ? '' : val.' '.g:airline_right_alt_sep.' '
+function! airline#parts#define_function(key, name)
+  call airline#parts#define(a:key, { 'function': a:name })
+endfunction
+
+function! airline#parts#define_text(key, text)
+  call airline#parts#define(a:key, { 'text': a:text })
+endfunction
+
+function! airline#parts#define_raw(key, raw)
+  call airline#parts#define(a:key, { 'raw': a:raw })
+endfunction
+
+function! airline#parts#get(key)
+  return get(s:parts, a:key, {})
 endfunction
 
 function! airline#parts#empty()

autoload/airline/util.vim

@@ -1,39 +1,12 @@
 " MIT License. Copyright (c) 2013 Bailey Ling.
 " vim: et ts=2 sts=2 sw=2
 
-function! s:get_val(part, append)
-  if has_key(g:airline_parts, a:part)
-    let val = g:airline_parts[a:part]
-    if match(val, '%\| ') > -1
-      return val
-    elseif a:append > 0
-      return '%{airline#parts#append("'.val.'")}'
-    elseif a:append < 0
-      return '%{airline#parts#prepend("'.val.'")}'
-    else
-      return '%{'.val.'()}'
-    endif
-  endif
-  return a:part
+function! airline#util#append(text)
+  return empty(a:text) ? '' : '  '.g:airline_left_alt_sep.' '.a:text
 endfunction
 
-function! airline#util#define_left_section(key, parts)
-  if !exists('g:airline_section_{a:key}') && len(a:parts) > 0
-    let g:airline_section_{a:key} = s:get_val(a:parts[0], 0)
-    for i in range(1, len(a:parts) - 1)
-      let g:airline_section_{a:key} .= s:get_val(a:parts[i], 1)
-    endfor
-  endif
-endfunction
-
-function! airline#util#define_right_section(key, parts)
-  if !exists('g:airline_section_{a:key}') && len(a:parts) > 0
-    let g:airline_section_{a:key} = ''
-    for i in range(0, len(a:parts) - 2)
-      let g:airline_section_{a:key} .= s:get_val(a:parts[i], -1)
-    endfor
-    let g:airline_section_{a:key} .= s:get_val(a:parts[-1], 0)
-  endif
+function! airline#util#prepend(text)
+  return empty(a:text) ? '' : a:text.' '.g:airline_right_alt_sep.' '
 endfunction
 
 if v:version >= 704