The Serde Data Model

Serde Data Model Types

The serde data model, as defined by the Serde Book, contains 29 types, each referred to as "A Serde Data Type".

1 - bool

A type capable of expressing exclusively the values true or false.

2 - i8

A signed integer type, capable of expressing any value in the range of -128..=127 (or -(2^7)..=((2^7) - 1)).

3 - i16

A signed integer type, capable of expressing any value in the range of -32768..=32767 (or -(2^15)..=((2^15) - 1)).

4 - i32

A signed integer type, capable of expressing any value in the range of -2147483648..=2147483647 (or -(2^31)..=((2^31) - 1)).

5 - i64

A signed integer type, capable of expressing any value in the range of -9223372036854775808..=9223372036854775807 (or -(2^63)..=((2^63) - 1)).

6 - i128

A signed integer type, capable of expressing any value in the range of -170141183460469231731687303715884105728..=170141183460469231731687303715884105727 (or -(2^127)..=((2^127) - 1)).

7 - u8

An unsigned integer type, capable of expressing any value in the range of 0..=255 (or 0..=((2^8) - 1)).

8 - u16

An unsigned integer type, capable of expressing any value in the range of 0..=65535 (or 0..=((2^16) - 1)).

9 - u32

An unsigned integer type, capable of expressing any value in the range of 0..=4294967295 (or 0..=((2^32) - 1)).

10 - u64

An unsigned integer type, capable of expressing any value in the range of 0..=18446744073709551615 (or 0..=((2^64) - 1)).

11 - u128

An unsigned integer type, capable of expressing any value in the range of 0..=340282366920938463463374607431768211456 (or 0..=((2^128) - 1)).

12 - f32

A "binary32" type defined as defined in IEEE 754-2008.

13 - f64

A "binary64" type defined as defined in IEEE 754-2008.

14 - char

A four-byte type representing a Unicode scalar value.

A Unicode scalar value is defined by Unicode 14.0 Chapter 3 Section 9 - "Unicode Encoding Forms", Definition D76:

Unicode scalar value: Any Unicode code point except high-surrogate and low-surrogate code points.

As a result of this definition, the set of Unicode scalar values consists of the ranges 0x0000_0000 to 0x0000_D7FF and 0x0000_E000 to 0x0010_FFFF inclusive.

15 - string

A type representing a variable quantity of bytes, which together represent a valid UTF-8 code point sequence, as defined by Unicode 14.0 Chapter 3 Section 9 - "Unicode Encoding Forms", Definition D92:

UTF-8 encoding form: The Unicode encoding form that assigns each Unicode scalar value to an unsigned byte sequence of one to four bytes in length, as specified in Table 3-6 and Table 3-7.

This encoding form is stored using the "UTF-8 encoding scheme", as defined by Unicode 14.0 Chapter 3 Section 10 - "Unicode Encoding Schemes", Definition D95:

UTF-8 encoding scheme: The Unicode encoding scheme that serializes a UTF-8 code unit sequence in exactly the same order as the code unit sequence itself.

16 - byte array

A type representing a variable quantity of bytes.

17 - option

A type representing zero or one Serde Data Type.

18 - unit

A type representing an anonymous value containing no data.

19 - unit_struct

A type representing a named value containing no data.

20 - unit_variant

A type representing a named, tagged union variant, containing no data.

21 - newtype_struct

A type representing a named value, containing exactly one anonymous Serde Data Type.

22 - newtype_variant

A type representing a named, tagged union variant, containing exactly one anonymous Serde Data Type.

23 - seq

A type representing a variable quantity of values of a single Serde Data Type, e.g. a "Homogeneous Array".

Values of each element of the seq may have differing values.

24 - tuple

A type representing a fixed quantity of values, each of any Serde Data Type, e.g. a "Heterogeneous Array".

Values of each element of the tuple may have differing values.

25 - tuple_struct

A type representing a named type specifically containing exactly one tuple Serde Data Type

26 - tuple_variant

A type representing a named, tagged union variant, containing exactly one tuple Serde Data Type.

27 - map

A type representing a variable quantity of key-value pairs. All keys are values of a single Serde Data Type. All values are a values of a single Serde Data Type.

28 - struct

A type representing a fixed quantity of named values, each of any Serde Data Type.

Values of each element of the tuple may have differing values.

NOTE: Similar to tuples , structs have a known number of members, however all members of a struct also have a known name.

structs are also similar to maps, in that each member has a name (as a key) and a value, however structs always have a fixed number of members, and their names are always constant.

29 - struct_variant

A type representing a named, tagged union variant, containing exactly one struct Serde Data type

Meta types

Named and Anonymous types

The above discussion differentiates between "named types" and "anonymous types".

"named types" are used to describe types that are bound to a name within the data type they are contained, such as a field of a struct.

"anonymous types" are used to describe types that are NOT bound to a name within the data type they are contained, such as a single element of a tuple.

enums or Tagged Unions

In the Rust language, the enum type (also known as "tagged unions" in other languages) describes a type that has a differing internal type based on a value known as a discriminant.

In the serde data model (as well as the rust language) discriminants are always of the type u32.

In the serde data model, the "internal type" of an enum can be one of any of the following:

• unit_variant
• newtype_variant
• tuple_variant
• struct_variant

References