Named Structs¶

A Named Struct is a special type construct that combines: * A Struct type * A list of names for the fields in the Struct, in depth-first search order

The depth-first search order for names arises from the the ability to nest Structs within other types. All Struct fields must be named, even nested fields.

Named Structs are most commonly used to model the schema of Read relations.

Determining Names¶

When producing/consuming names for a NamedStruct, some types require special handling:

Struct¶

A struct has names for each of its inner fields.

For example, the following Struct

struct<i64, i64>
       ↑    ↑
       a    b

has 2 names, one for each of its inner fields.

Structs within Compound Types¶

Struct types nested in compound types must also be be named.

Structs within Maps¶

If a Map contains Structs, either as keys or values or both, the Struct fields must be named. Keys are named before values. For example the following Map

map<struct<i64, i64>, struct<i64, i64, i64>>
           ↑    ↑            ↑    ↑    ↑
           a    b            c    d    e

has 5 named fields * 2 names [a, b] for the struct fields used as a key * 3 names [c, d, e] for the struct fields used as a value

Structs within List¶

If a List contains Structs, the Struct fields must be named. For example the following List

list<struct<i64, i64>>
            ↑    ↑
            a    b

has 2 named fields [a, b] for the struct fields.

Structs within Struct¶

Structs can also be embedded within Structs.

A Struct like

struct<struct<i64, i64>, struct<i64, i64, i64>>
       ↑      ↑    ↑     ↑      ↑    ↑    ↑
       a      b    c     d      e    f    g

has 7 names * 1 name [a] for the 1^st nested struct field * 2 names [b, c] for the fields within the 1^st nested struct * 1 name [d] the for the 2^nd nested struct field * 3 names [e, f, g] for the fields within the 2^nd nested struct

Putting It All Together¶

Simple Named Struct¶

NamedStruct {
    names: [a, b, c, d]
    struct: struct<i64, list<i64>, map<i64, i64>, i64>
                   ↑    ↑          ↑              ↑
                   a    b          c              d
}

Structs in Compound Types¶

NamedStruct {
    names: [a, b, c, d, e, f, g, h]
    struct: struct<i64, list<struct<i64, i64>>, map<i64, struct<i64, i64>>, i64>
                   ↑    ↑          ↑     ↑      ↑               ↑    ↑      ↑
                   a    b          c     d      e               f    g      h
}

Structs in Structs¶

NamedStruct {
    names: [a, b, c, d, e, f, g, h, i]
    struct: struct<i64, struct<i64, struct<i64, i64>, i64, struct<i64, i64>>>>
                   ↑    ↑      ↑    ↑      ↑    ↑     ↑    ↑      ↑    ↑
                   a    b      c    d      e    f     g    h      i    j
}