Advanced Usage Of Blocks

This section describes how Block conversion methods are selected and how they interact with variable metadata and transactions.

Model-Driven Method Dispatch

Variable does not hardcode a single getter/setter implementation. Instead, it binds function pointers to specific Block methods based on the variable model and size constraints.

Typical mapping:

Model	C++ path	Python path	Notes
Bytes	set/getByteArray	set/getByteArrayPy	Raw byte semantics.
UInt	set/getUInt	set/getUIntPy	Uses byte-array/PyFunc fallback when >64-bit
Int	set/getInt	set/getIntPy	Uses byte-array/PyFunc fallback when >64-bit
Bool	set/getBool	set/getBoolPy	Bit-width usually 1.
String	set/getString	set/getStringPy	Byte payload interpreted as string.
Float	set/getFloat	set/getFloatPy	32-bit float conversion.
Double	set/getDouble	set/getDoublePy	64-bit float conversion.
Fixed	set/getFixed	set/getFixedPy	Uses binary-point metadata.
PyFunc	(Python-focused)	set/getPyFunc	Delegates conversion to model hooks.

Conversion vs Transaction

The Block API has two layers:

• Conversion layer: set*/get* methods convert between native types and staged block bytes.

• Transaction layer: write/read/startTransaction/checkTransaction moves staged bytes to and from hardware.

In the C++ Variable API, a typed set call performs both steps:

1. Conversion into staged bytes via bound Block method.

2. Block::write() (write + verify/check sequence).

A typed get call similarly performs:

1. Block::read().

2. Conversion from staged bytes via bound Block method.

Packing Rules and Variable Layout

The internal setBytes/getBytes helpers are used by all typed methods and apply variable layout metadata:

• Bit offsets and bit sizes (including disjoint fields)

• List semantics (numValues, valueStride)

• Fast contiguous byte-copy optimization when possible

• Byte reversal and bit-order constraints

Because every typed method funnels through these helpers, custom subclasses can extend behavior while preserving the same packing model.