`rethrow` — Rethrow a caught exception so it propagates to an outer handler.

rethrow re-raises an exception so an outer catch block or embedding runtime can handle it. Passing an MException preserves identifier and message, while passing text creates a new error payload; rethrow() in a catch block rethrows the active exception context.

Syntax

rethrow(err)

Inputs

Name	Type	Required	Default	Description
`err`	`Any`	Yes	—	Error value to rethrow.

How `rethrow` works

rethrow(err) preserves the identifier and message of an MException value.
rethrow(message) raises a fresh error using the supplied string as the message.
Other value types produce a generic RunMat:error-style failure describing the value.
rethrow never returns normally; it immediately transfers control outward to the next enclosing error handler.
In Ignition catch blocks, rethrow() with no argument uses the most recently caught exception.

Does RunMat run `rethrow` on the GPU?

rethrow performs no provider dispatch; it raises or propagates a host-side runtime error immediately.

GPU memory and residency

rethrow is control flow only and never executes on the GPU.

Examples

Propagate an exception to an outer catch block

try
    try
        error("RunMat:demo:badInput", "Bad input.");
    catch err
        rethrow(err);
    end
catch outer
    disp(outer.identifier)
end

Expected output:

RunMat:demo:badInput

Use the no-argument shorthand inside an Ignition catch block

try
    try
        error("RunMat:oops", "x");
    catch
        rethrow();
    end
catch err
    disp(err.message)
end

Expected output:

Using `rethrow` with coding agents

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

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

FAQ

When should I use rethrow instead of error?⌄

Use rethrow when you want to propagate the current exception rather than constructing a new one from scratch.

Does rethrow(err) preserve the original identifier?⌄

Yes. When err is an MException, RunMat preserves both the identifier and the message.

Is rethrow() without an argument supported?⌄

Yes in Ignition catch-block execution, where it reuses the most recently caught exception.

assert · error · warning

Open-source implementation

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

View the source for rethrow 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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rethrow — Rethrow a caught exception so it propagates to an outer handler.