`subsref` — Dispatch overloaded object indexing operations to class-specific `Class.subsref` implementations.

subsref(obj, kind, payload) is the internal dispatch builtin for overloaded object indexing. MATLAB-style field, paren, and brace indexing lowers to this mechanism, which resolves class-specific Class.subsref handlers.

Syntax

out = subsref(obj, kind, payload)

Inputs

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

Returns

Name	Type	Description
`out`	`Any`	Indexed value.

Errors

Identifier	When	Message
`RunMat:InvalidObjectDispatch`	Receiver is not an object or handle object.	`subsref: requires object receiver`
`RunMat:MissingSubsref`	Target class does not implement subsref.	`subsref: class does not define subsref for indexing operation`

How `subsref` works

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

Does RunMat run `subsref` on the GPU?

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

GPU memory and residency

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

Examples

Index a datetime array explicitly

t = datetime([2024 2025], [1 6], [15 20]);
item = subsref(t, "()", {2})

Expected output:

item =
  20-Jun-2025 00:00:00

Read a datetime property explicitly

t = datetime(2024, 4, 9);
fmt = subsref(t, ".", "Format")

Expected output:

fmt =
    'dd-MMM-yyyy HH:mm:ss'

Using `subsref` with coding agents

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

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

FAQ

Should I call subsref directly in normal code?⌄

Usually no. Prefer ordinary syntax like obj.field or obj(2). 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 subsref actually do?⌄

It resolves the receiver's class and forwards the operation to that class's Class.subsref implementation.

subsasgn

Open-source implementation

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

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

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subsref — Dispatch overloaded object indexing operations to class-specific Class.subsref implementations.