When an error occurs in a try block, MATLAB transfers control to the catch block. If the catch block has an identifier, MATLAB enters the catch block with the identifier set to an MException object that contains the error message, the message ID, and the stack trace. You can use this object with functions such as rethrow to pass the error to the code that called it. Not only does the object always contain information about the correct error, there is no longer any need to save the lasterr around the try/catch block to avoid breaking old code. For more information, see “Capturing Information About the Error”.

Use an identifier on the catch block. If the catch block has an identifier, the state of lasterr and lasterror are unchanged. Typically, you can replace a call to lasterror with the catch block identifier, and you can replace a call to lasterr by referencing the message field of this identifier. You can probably remove any code that saves the previous state of lasterr and lasterror. The resulting code is typically smaller, clearer, and faster than the older code.