Empty key in JSON

[Yukihiro Nakadaira]

:echo jsondecode('{"":"x"}')
E713: Cannot use empty key for Dictionary

Will Vim allow empty key?

--

Yukihiro Nakadaira - yukihiro....@gmail.com

[Bram Moolenaar]

Yukihiro Nakadaira wrote:

> :echo jsondecode('{"":"x"}')
> E713: Cannot use empty key for Dictionary
>
> Will Vim allow empty key?

Hmm, if you take the standard literally I suppose it allows for an empty
key. In practice it's an indication something went wrong.

Why are you asking, do you see a practical application for it?

The standard also allows for duplicate names, even though in practice
that doesn't work. So even though it's valid JSON, it doesn't mean it's
a valid value after converting from JSON to Vim types.

So the error is actually correct, it's not saying the JSON is invalid,
it's saying the result in Vim types is invalid.

--
hundred-and-one symptoms of being an internet addict:
40. You tell the cab driver you live at
http://123.elm.street/house/bluetrim.html
41. You actually try that 123.elm.street address.

/// Bram Moolenaar -- Br...@Moolenaar.net -- http://www.Moolenaar.net \\\
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[Yukihiro Nakadaira]

On Tue, Jan 26, 2016 at 10:29 PM, Bram Moolenaar <Br...@moolenaar.net> wrote:

Yukihiro Nakadaira wrote:

> :echo jsondecode('{"":"x"}')
> E713: Cannot use empty key for Dictionary
>
> Will Vim allow empty key?

Hmm, if you take the standard literally I suppose it allows for an empty
key.  In practice it's an indication something went wrong.

Why are you asking, do you see a practical application for it?

I don't know practical example in JSON.

In Vim script, counting line is a possible example.

let d = {}
for line in getline(1, '$')
  let d[line] = get(d, line, 0) + 1
endfor
for line in getline(1, '$')
  if d[line] == 1
    do something
  else
    do something
  endif
endfor

Patience diff algorithm uses such a method, for example.

https://github.com/ynkdir/vim-diff/blob/master/autoload/diff/patience.vim

Although, there is a workaround like d['x'.line] = ...

The standard also allows for duplicate names, even though in practice
that doesn't work.  So even though it's valid JSON, it doesn't mean it's
a valid value after converting from JSON to Vim types.

So the error is actually correct, it's not saying the JSON is invalid,
it's saying the result in Vim types is invalid.

I see.

--

Yukihiro Nakadaira - yukihiro....@gmail.com

[Nikolay Aleksandrovich Pavlov]

2016-01-26 16:29 GMT+03:00 Bram Moolenaar <Br...@moolenaar.net>:
>
> Yukihiro Nakadaira wrote:
>
>> :echo jsondecode('{"":"x"}')
>> E713: Cannot use empty key for Dictionary
>>
>> Will Vim allow empty key?
>
> Hmm, if you take the standard literally I suppose it allows for an empty
> key. In practice it's an indication something went wrong.
>
> Why are you asking, do you see a practical application for it?

In addition to diffing there is also caching: imagine function that
compiles PCRE regex into Vim regex (or fallback implementation for
glob2regpat() for older Vim versions). Using dictionaries for caching
is natural and empty pattern is also the valid one. I do not see why
this restriction exists in first place, most of dictionary
implementations allow empty strings simply because *not* allowing it
requires additional length checks which will not be written without a
good reason.

>
> The standard also allows for duplicate names, even though in practice
> that doesn't work. So even though it's valid JSON, it doesn't mean it's
> a valid value after converting from JSON to Vim types.

Standard states this is implementation-defined (though in place of one
sentence and using this exact term they have written a whole paragraph
with this meaning). In any case “internal error” is not something that
should be reported in this case, documentation explicitly states that
internal error is a bug.

>
> So the error is actually correct, it's not saying the JSON is invalid,
> it's saying the result in Vim types is invalid.
>
> --
> hundred-and-one symptoms of being an internet addict:
> 40. You tell the cab driver you live at
> http://123.elm.street/house/bluetrim.html
> 41. You actually try that 123.elm.street address.
>
> /// Bram Moolenaar -- Br...@Moolenaar.net -- http://www.Moolenaar.net \\\
> /// sponsor Vim, vote for features -- http://www.Vim.org/sponsor/ \\\
> \\\ an exciting new programming language -- http://www.Zimbu.org ///
> \\\ help me help AIDS victims -- http://ICCF-Holland.org ///
>

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