MATLAB: “clear all” causing annoying warning messages

clear allcontains matlab code that is currently executingwarning

I am using "clear all" at the start of a ".m" file that I have written myself (lets call it "myfile.m"). When I run the file, I get three identical messages stating "Warning: The file 'myfile.m' could not be cleared because it contains MATLAB code that is currently executing." I don't want to turn warnings off, because I am writing my own warnings later in the file. Why does this happen and how can I prevent it? I am using Matlab version 2017a.

Best Answer

clear all clears Matlab's memory in a brutal way. While removing all locally used variables might be useful for scripts, which are short hacks or prooves of concept, it is evil is productive code. Prefer clean workspaces by using functions instead.
Then clear all deletes all functions from the RAM, and the reloading from the slow hard disk wastes a lot of time. Doing this frequently means a massive loss of speed. In your case Matlab warns, that some functions cannot be removed. Perhaps they are callbacks of GUIs or timers, or the currently processed M-code.
In addition all persistent variables are cleared and many functions need a time-consuming re-initialization afterwards.
In older Matlab versions clear all has deleted all debugger breakpoints also, and anything, which impedes debugging is an enemy of teh programmer.
The solution is trivial: Omit the evil clear all. Instead of hiding the warning message, this is much more efficient.
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