Toml: Nested arrays of tables

[yasammez]

Hi everyone!

TOML has arrays:

array = [ [1, 0], [0, 1] ]

"array":[ [ 1, 0], [0, 1] ]

TOML has tables:

[table]
value = 1

"table":{ "value":1 }

TOML even has arraytables:

[[arraytable]]
value = 1
[[arraytable]]
value = 2

"arraytable":[ { "value":1 }, { "value":2} ]

But is there any way to do something like

"nested_array_table":[ 
  [ { "value":1 }, {"value":0} ], 
  [ {"value":0}, {"value":1, "comment":"bottom right diagonal element"} ] ]

in TOML? If so, how can I do this? If not, why can't I do this?

I understand that there is always a way around this, by for instance flattening arrays

[[matrix]]
value = 1
[[matrix]]
value = 0
[[matrix]]
value = 1
[[matrix]]
value = 0
comment = "bottom right diagonal element"

or introducing _filler_ structs:

[[matrix.row]]
  [[matrix.row.column]]
  value = 1
  [[matrix.row.column]]
  value = 0
[[matrix.row]]
  [[matrix.row.column]]
  value = 1
  [[matrix.row.column]]
  value = 0
  comment = "bottom right diagonal element"

However, none of these seems really appropriate. Also, in that case, TOML would be strict less expressive than JSON, which is kind of a pitty, since JSON is so darn unreadable.

[yasammez]

One possible idea for an extension, which, I admit, scales not very well, would be to add additional layers of brackets around the table names: one for each level of array depth:

[[[matrix]]]
value = 1
[[matrix]]
value = 0
[[[matrix]]]
value = 0
[[matrix]]
value = 1
comment = "bottom right diagonal element"

This would be equivalent to the following JSON:

"matrix":[ [ { "value":1 }, { "value":0 } ], [ { "value":0 }, { "value":1, "comment":"bottom right diagonal element" } ] ]

[sanmai-NL]

Why does the lack of a matrix notation make TOML strictly less expressive than JSON? I'm interested to know, since I'm not aware of any such notation in JSON.

[ChristianSi]

@fischmax: TOML has inline tables, so you should be able to write your example as follows (I think):

nested_array_table = [ 
    [ {value = 1}, {value = 0} ], 
    [ {value = 0}, {value = 1, comment = "bottom right diagonal element"} ] ]

[FranklinYu]

In #309 @jodastephen suggested an alternative grammar for array table:

[analyzers.filter]
  [#]
  type = "icu-tokenizer"

  [#]
  type = "lowercase"

  [#]
  type = "length"
  min = 2
  max = 35

If this is accepted, it can be easily extended to allow n-dimension matrix:

[nested_array_table]
  [#]
    [##]
    value = 1
    [##]
    value = 0

  [#]
    [##]
    value = 0
    [##]
    value = 1
    comment = "bottom right diagonal element"

[nikitindiz]

Any workaround?

[pradyunsg]

IMO, this issue is a duplicate of #309. It can be closed in favour of that.

[pradyunsg]

Closing as a duplicate of #309.