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
kindargument selects the assignment form:'.','()', or'{}'. - For dot assignment,
payloadis typically a field/property name string. - For
()and{}assignment,payloadis typically a cell array of indices. - The builtin forwards the assignment to the receiver's class-specific
Class.subsasgnimplementation and returns the updated object value. - Integer selectors and assigned values retain their native class, exact value, shape, and resident handle during dispatch. The class method owns assignment conversion, overflow, and returned-receiver semantics.
- Prefer normal assignment syntax in user code; direct calls to
subsasgnare 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:
2024-04-09Replace 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 00:00:00Using 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.
Related Oop functions
Indexing
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
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