subsasgn — Dispatch object assignment requests to a class-specific Class.subsasgn implementation.

subsasgn(obj, kind, payload, rhs) is the advanced builtin that RunMat uses to implement overloaded indexed assignment on objects and handle objects. Normal syntax such as obj.field = value, obj(2) = value, and obj{1} = value generally lowers to this mechanism automatically. The global builtin resolves the receiver's class name and forwards the assignment to Class.subsasgn.

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.

How RunMat runs 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

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

Open-source implementation

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

• View subsasgn.rs on GitHub
• Learn how the runtime works
• Found a bug? Open an issue with a minimal reproduction.

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