Examples

These snippets match the generated types in tests/generated. Build them with mojo run -I src -I tests/generated.

Owned round trip

encode_Message builds a buffer whose root is a Message. decode_Message copies the fields out.

from benchmark_v2 import Message, decode_Message, encode_Message

var msg = Message()
msg.f_bool = True
msg.f_int32 = 150
msg.f_string = "hi"
var buf = encode_Message(msg)
var back = decode_Message(buf)

Fields that still hold their schema default are left out of the buffer. f_bool_2 stays false and is not stored. Read it back and you get false again.

A view over the same bytes

from benchmark_v2 import view_Message

var view = view_Message(buf)
var n = view.f_int32()
var text = view.f_string()

f_int32 reads four bytes at the vtable offset. f_string copies the UTF-8 bytes out because a Mojo String owns its storage. The integer read does not allocate.

Nested tables and vectors

from benchmark_v2 import Document, DocumentItem, encode_Document

var doc = Document()
doc.id = "d1"
doc.has_meta = True
doc.meta.region = "us"
var item = DocumentItem()
item.sku = "ab"
item.qty = 4
doc.items.append(item^)
var bytes = encode_Document(doc)

has_meta is the presence bit. Leave it false and the meta table is absent. An empty items list is also absent. A list of length one is a vector of table offsets.

Structs, unions, and optional scalars

from std.collections import Optional
from features import Holder, Item_Text, encode_Holder

var h = Holder()
h.has_point = True
h.point.x = 1.5
h.point.y = -2.0
h.item_type = Item_Text
h.item_Text.value = "hello"
h.maybe = Optional(Int32(0))

Point is inline. Its eight bytes sit inside Holder, not behind an offset. maybe is optional, so zero is stored. A missing maybe would be None, which is a different value from zero.

item_type selects which table was packed. Item_Text is the generated name of that union member.

FlexBuffers

from flex.builder import FlexBuilder
from flex.reader import flex_loads

var b = FlexBuilder()
var start = b.start_vector()
b.int(1)
b.int(2)
b.int(3)
b.end_vector(start)
var tree = flex_loads(b.finish())

tree.kind() is the root type. For a map, tree.find(tree.root, "harbor") returns the child index. The official gold buffer in the test suite is read the same way.