Ken Takata wrote:
> 2016/7/30 Sat 5:38:42 UTC+9 Bram Moolenaar wrote:
> > Patch 7.4.2120
> > Problem: User defined functions can't be a closure.
> > Solution: Add the "closure" argument. Allow using :unlet on a bound
> > variable. (Yasuhiro Matsumoto, Ken Takata)
> > Files: runtime/doc/eval.txt, src/testdir/test_lambda.vim,
> > src/userfunc.c,
> > src/eval.c src/proto/userfunc.pro
>
> I had a report that this patch doesn't work as expected:
>
> function! Foo()
> let x = 0
> function! Bar() closure
> let x += 1
> return x
> endfunction
> return function('Bar')
> endfunction
>
> let Count = Foo()
> echo Count() " => 1
> echo Count() " => 2
> echo Count() " => 3
>
> let Count2 = Foo()
> echo Count() " => 1 (Should be 4)
Calling Foo() creates a new context in which "x" is set to zero.
And a new Bar() is created that uses this "x". It should not re-use the
existing Bar(), it is still in use, being referenced.
Thus where it says: /* redefine existing function */
It should leave that function alone and create a new one. But the new
Bar() must be the one that's found in the global scope. Thus it's a mix
of defining a new function and replacing an existing one.
> The function Bar() should have been handled like a lambda function which means
> reference counting is needed.
> Using a dict function with closure works as expected:
>
> function! Foo()
> let x = 0
> let d = {}
> function! d.Bar() closure
> let x += 1
> return x
> endfunction
> return d.Bar
> endfunction
>
> (But this might be not so useful.)
> I don't have a good idea to fix this problem. Current idea is:
>
> * "function! Bar() closure" creates an unnamed function with the internal name
> "<lambda>N", and
> * The Funcref is assign to a local variable "Bar".
>
> Not sure this goes well...
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