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``cfg.decode_save_metatables``
Specify whether to set metatables for all arrays and maps
**Sparse arrays features**
During encoding, the MsgPack encoder tries to classify tables into one of four kinds:
map - at least one table index is not unsigned integer
regular array - all array indexes are available
sparse array - at least one array index is missing
excessively sparse array - the number of values missing exceeds the configured ratio
An array is excessively sparse when **all** the following conditions are met:
``encode_sparse_ratio`` > 0
``max(table)`` > ``encode_sparse_safe``
``max(table)`` > ``count(table)`` * ``encode_sparse_ratio``
MsgPack encoder never considers an array to be excessively sparse when ``encode_sparse_ratio = 0``. The ``encode_sparse_safe`` limit ensures that small Lua arrays are always encoded as sparse arrays. By default, attempting to encode an excessively sparse array generates an error. If ``encode_sparse_convert`` is set to ``true``, excessively sparse arrays will be handled as maps.
**msgpack.cfg() example 1:**
If ``msgpack.cfg.encode_invalid_numbers = true`` (the default), then NaN and Inf are legal values. If that is not desirable, then ensure that ``msgpack.encode()`` does not accept them, by saying ``msgpack.cfg{encode_invalid_numbers = false}``, thus:
tarantool> msgpack = require('msgpack'); msgpack.cfg{encode_invalid_numbers = true}
---
...
tarantool> msgpack.decode(msgpack.encode{1, 0 / 0, 1 / 0, false})
---
- [1, -nan, inf, false]
- 22
...
tarantool> msgpack.cfg{encode_invalid_numbers = false}
---
...
tarantool> msgpack.decode(msgpack.encode{1, 0 / 0, 1 / 0, false})
---
- error: ... number must not be NaN or Inf'
...
**msgpack.cfg() example 2:**
To avoid generating errors on attempts to encode unknown data types as userdata/cdata, you can use this code:
tarantool> httpc = require('http.client').new()
---
...

tarantool> msgpack.encode(httpc.curl)
---
- error: unsupported Lua type 'userdata'
...

tarantool> msgpack.cfg{encode_use_tostring = true}
---
...

tarantool> msgpack.encode(httpc.curl)
---
- !!binary tnVzZXJkYXRhOiAweDAxMDU5NDQ2Mzg=
...
To achieve the same effect for only one call to ``msgpack.encode()`` (that is without changing the configuration permanently), you can use ``msgpack.new({encode_invalid_numbers = true}).encode({1, 2})``.
Similar configuration settings exist for :ref:`JSON <json-module_cfg>` and :ref:`YAML <yaml-cfg>`.
A value comparable to Lua "nil" which may be useful as a placeholder in a tuple.
**Example**
tarantool> msgpack = require('msgpack')
---
...
tarantool> y = msgpack.encode({'a',1,'b',2})
---
...
tarantool> z = msgpack.decode(y)
---
...
tarantool> z[1], z[2], z[3], z[4]
---
- a
- 1
- b
- 2
...
tarantool> box.space.tester:insert{20, msgpack.NULL, 20}
---
- [20, null, 20]
...
**Since:** :doc:`2.10.0 </release/2.10.0>`
Encode an arbitrary Lua object into the MsgPack format.
a Lua object of any type.
encoded MsgPack data encapsulated in a MsgPack object.
userdata
local msgpack = require('msgpack')

-- Create a MsgPack object from a Lua object of any type
local mp_from_number = msgpack.object(123)
local mp_from_string = msgpack.object('hello world')
local mp_from_array = msgpack.object({ 10, 20, 30 })
local mp_from_table = msgpack.object({ band_name = 'The Beatles', year = 1960 })
local mp_from_tuple = msgpack.object(box.tuple.new(1, 'The Beatles', 1960))
Create a MsgPack object from a raw MsgPack string.

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testing_project / Documentation: reference/reference_lua/msgpack — English

tarantool> msgpack = require('msgpack'); msgpack.cfg{encode_invalid_numbers = true}
---
...
tarantool> msgpack.decode(msgpack.encode{1, 0 / 0, 1 / 0, false})
---
- [1, -nan, inf, false]
- 22
...
tarantool> msgpack.cfg{encode_invalid_numbers = false}
---
...
tarantool> msgpack.decode(msgpack.encode{1, 0 / 0, 1 / 0, false})
---
- error: ... number must not be NaN or Inf'
...
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