In Simulink, are Goto and From blocks generally considered bad style?
goto, matlab, simulink, styles
Solution
The Mathworks Automotive Advisory Board has published some modeling guidelines (PDF) that include usage of `Goto`/`From`. The rules they list are:
Do not have subsystems that are floating, i.e. all inputs / output ports are connected via `Goto`s. One of the great things about Simulink is the ability to determine signal flow with only a cursory visual inspection, do not destroy this by linking everything with `Goto`s. At least have one feed-forward and one feedback loop between subsystems connected by signal lines.
- My personal opinion on feedback signals is that they should all be connected with signal lines, but I'm sure you can come up with cases where drawing all of them clutters the model.
The second guideline is about the scope of the `Goto` tag; keep the visibility `local` as much as possible.
- I feel setting visibility to `scoped` is acceptable also as long as you're not using the matching `From` more than a couple of levels downstream from the `Goto`. I've yet to come across a legitimate need for a global `Goto` tag.
So, all `Goto` usage isn't bad, and you're right that it can improve readability in some cases. That being said, I don't think Gotos are justified for the picture above. I realize it is just an example, but I should point out that if the buses being created are virtual that order of the inputs at the creator doesn't matter, and rearranging Bus Create and Mux block inputs can work wonders for readability.
The problem with the guidelines above are that there's room for bending them, and developers on your team might do just that. Even if everyone is diligent about following them at first, you may run afoul of these guidelines one day, a long time from now, when you redraw that section of the model for refining / adding functionality. Rearranging inputs and outputs can be especially irritating in middle of implementing some cool new feature. That may be the reason your employer chose to impose a blanket ban. It is inconvenient in some cases, but is easier to enforce.
Problem
I was working on a Simulink model recently and was using `Goto` and `From` blocks to keep a very busy system from becoming a twisted mess of wires. I was informed that I was not to use `Goto` and `From` blocks as they are considered bad style (at least, according to my employer). While I hold that wires should be kept connected whenever possible, I believe that `Goto` and `From` blocks can significantly improve the readability of a system/subsystem if the model would result in lots of crossed wires otherwise; especially if the blocks can be color-coded (e.g. purple `Goto` block goes to all the purple `From` blocks). I'd supply an image of the subsystem I'm working with, but I'm not sure I can put it on here. The subsystem itself has about 12 subsystem blocks (and possibly more later) within it, each with two bus-type outputs. The first output of each subsystem goes to a `Bus Creator` block, and the second output of each goes to a second `Bus Creator` block. Since the subsystem are aligned vertically and the `Bus Creator`s are to the right, this results in many crossed wires. I was using `Goto` and `From` blocks to clean up the system. I can supply an image of a smaller, but similar model that I put together for this question. For a system with on the order of 12 subsystems, this becomes very busy. I was using `Goto` and `From` blocks to connect the subsystems and the `Bus Creator`s without a plethora of crossed wires. I believe my employer may be carrying the stigma of using `goto` statements from text-based languages and applying it to `Goto`/`From` blocks in Simulink. Generally speaking, is using `Goto` and `From` blocks in this way (or any way) considered to be bad style?