`subsasgn` — Dispatch overloaded object assignment operations to class-specific `Class.subsasgn` implementations.

subsasgn(obj, kind, payload, rhs) is the internal dispatch builtin for overloaded indexed assignment on objects. MATLAB-style assignment syntax lowers to this mechanism, which resolves class-specific Class.subsasgn handlers.

Syntax

obj = subsasgn(obj, kind, payload, rhs)

Inputs

Name	Type	Required	Default	Description
`obj`	`Any`	Yes	—	Object receiver.
`kind`	`StringScalar`	Yes	—	Indexing kind token ('()', '{}', '.').
`payload`	`Any`	Yes	—	Indexing payload.
`rhs`	`Any`	Yes	—	Assigned value.

Returns

Name	Type	Description
`obj`	`Any`	Updated object value.

Errors

Identifier	When	Message
`RunMat:InvalidObjectDispatch`	Receiver is not an object or handle object.	`subsasgn: requires object receiver`
`RunMat:MissingSubsasgn`	Target class does not implement subsasgn.	`subsasgn: class does not define subsasgn for indexed assignment`

How `subsasgn` works

The receiver must be an object or handle object.
The kind argument selects the assignment form: '.', '()', or '{}'.
For dot assignment, payload is typically a field/property name string.
For () and {} assignment, payload is typically a cell array of indices.
The builtin forwards the assignment to the receiver's class-specific Class.subsasgn implementation and returns the updated object value.
Prefer normal assignment syntax in user code; direct calls to subsasgn are mainly useful for advanced dispatch or testing.

Does RunMat run `subsasgn` on the GPU?

subsasgn performs no provider dispatch; it forwards assignment requests to the appropriate class-specific host implementation.

GPU memory and residency

subsasgn is host-side object dispatch and does not itself manage GPU residency.

Examples

Change a datetime display format explicitly

t = datetime(2024, 4, 9);
t = subsasgn(t, ".", "Format", "yyyy-MM-dd");
disp(t)

Expected output:

2024-04-09

Replace one element of a datetime array explicitly

t = datetime([2024 2025], [1 6], [15 20]);
t = subsasgn(t, "()", {2}, datetime(2030, 1, 1));
disp(t)

Expected output:

15-Jan-2024 00:00:00
01-Jan-2030 00:00:00

Using `subsasgn` with coding agents

Open a RunMat example with live inputs, then ask the agent to explain how subsasgn changes the result.

Run a small subsasgn example, explain the result, then change one input and compare the output.

FAQ

Should I call subsasgn directly in normal code?⌄

Usually no. Prefer ordinary assignment syntax like obj.field = value or obj(2) = value. Direct calls are mainly for advanced dispatch and testing.

What values can kind take?⌄

RunMat's object-dispatch path expects '.', '()', or '{}'.

What does the global subsasgn actually do?⌄

It resolves the receiver's class and forwards the assignment to that class's Class.subsasgn implementation.

subsref

Open-source implementation

Unlike proprietary runtimes, every RunMat function is open-source. Read exactly how subsasgn is executed, line by line, in Rust.

View the source for subsasgn in Rust on GitHub
Learn how the RunMat runtime works
Found a bug? Open an issue with a minimal reproduction.

About RunMat

RunMat is an open-source runtime that executes MATLAB-syntax code blazing on any GPU. It is licensed under the Apache 2.0 license.

RunMat automatically optimizes your math for GPU execution on Apple, Nvidia, and AMD hardware. No code changes needed. Simulations that took hours now take minutes.
Start running code in seconds. RunMat runs in the browser, on the desktop, or from the CLI. No license server, no IT ticket.

Getting started · Benchmarks · Pricing

subsasgn — Dispatch overloaded object assignment operations to class-specific Class.subsasgn implementations.