lua-users home
lua-l archive

[Date Prev][Date Next][Thread Prev][Thread Next] [Date Index] [Thread Index]

On Mon, Jul 15, 2019, 11:47 AM Sergey Kovalev <> wrote:

for auto,defer in scope() do
  defer(function() print"defer" end)
  local f=auto(io.close){ "scope54.lua"}

I think this is enough readable and looks nice.

This is still way less readable than

local <toclose> file, err ="myfile")
-- ...

However, you can simplify scope() a bit [1], allowing to write

for finally_close in scope() do
  local file, err ="myfile", "r")
  finally_close( file )
  -- ... 

That is clean enough to not make me miss <toclose>. I can also ignore the fact that the 4th iterator parameter itself is implementated as a <toclose> variable.

But with the last commits we got constant propagation, so I really want <const>. And if we already have annotatations probably <toclose> is worth too.

The annotation system is a considerable addition to the language and it may seem an overkill for a single use case. But it starts to make sense when multiple issues are accounted by it.

Who would endorse the metatables if them were used only for __gc?


[1] E.g.:

local function scope()
  local obj = {}

  local function mark_to_close( o )
      obj[1+#obj] = o
  local function closing()
      for i = 1, #obj do
          local m = getmetatable( obj[i] )
          if m and m.__toclose then
              m.__toclose( obj[i] )

  local function iter( n, c )
      if c == nil then return mark_to_close end
      return nil
  return iter, nil, nil, setmetatable({},{__close=closing})