Matlab Strict Mode?

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Paul
Paul 2016-10-11
编辑： Jan 2017-4-19
Can we please have a "strict mode" in Matlab, which does not guess what you mean, but instead does things consistently? Take this example:
x = (3:7)';
size(x([1; 2; 2; 3; 3; 4])) % 6 x 1
size(x([1 2; 2 3; 3 4])) % 3 x 2
size(x([1 2 2; 3 3 4])) % 2 x 3
size(x([1 2 2 3 3 4])) % 6 x 1 !?!?
Just to be clear: if Matlab were consistent, the last result would be 1x6.
Code that runs on arbitrary input data, annoyingly, needs endless if-then blocks to compensate for Matlab's horrendous inconsistencies, making it slow to develop, cluttered, slow to run, and just a pain in general.
I understand Mathworks is probably not keen on breaking everybody's code in one language update.
But perhaps a simple "strict mode" (somewhat akin to Javascript's "use strict" directive at the top of files and functions) could trigger a consistent dimensions mode, and in general provide a more mature interpretation of the programming language?
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Kevin
Kevin 2017-4-19
I don't understand your objections, John. An opt-in "strict mode" doesn't have to break old code. Other languages do this successfully with something like a 'use strict' pragma at the top of source files.
If you don't want old code to break, or don't want to take responsibility for cleaning up old code that relies on ambiguous language features, then don't enable strict mode.
As a relative newcomer, I find it beyond frustrating when MATLAB allows me to clobber essential built-in functions like 'dist' or 'cluster' with no warnings, and then I get warnings like "Subscript indices must either be real positive integers or logicals" when I try to run the actual functions later on.
Sure, OK, that's a mistake I only have to make once or twice before I remember not to name variables 'dist' or 'cluster', but is "just learn the language"—all those hundreds of built-in functions, plus those from any toolboxes you have loaded—a good answer for your new users in this case? Answer: NO. And flagging weird, ambiguous, or bad language behavior (or keeping the user from shooting themself in the foot) is exactly what "strict" modes are supposed to do.
Walter Roberson
Walter Roberson 2017-4-19
A question comes up as to whether the effects of the strict pragma would carry through into routines that are called. If so then it is likely that deeper down calls would break. If not, then you might have to put the strict pragma in for each routine, which could be tedious. Perhaps it would be workable to "scope" such a pragma -- e.g., have it before the first "function" line if it is to apply to the file as a whole.

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Jan
Jan 2017-4-19
编辑：Jan 2017-4-19
A "strict mode" would not even break old code, but even the idea behind Matlab to allow to users to perform matrix operations conveniently. The complete "operate on the first non-singelton dimension" is not-strict:
m = mean(X)
s = sum(X)
without specifying the dimension to operate on. If X is a [nMeasuremenmts x nChannel] matrix and the number of measurements can be 1, the results may differ from the intention. What should happen with such commands in "strict" mode?
What about:
AxesH = axes;
plot(y)
This is a racing condition: when the use clicks in another figure after the axes command, but before the plot, the diagram appears in the wrong figure. "Strict" would be:
plot(y, 'Parent', AxesH)
Or perhaps: plot(AxesH, y)? No! Because this can fail in older Matlab versions, where the axes handles was a double and might (or should!) be misinterpreted as the x coordinate.
You find many such details, which allows users to be intentionally lazy. But this convenient programming style is prone to bugs in productive code. To write "strict" code, a strict-flag will not help, but only to specify each an every detail explicitely. This will and must slow down the code, but there is no way to let Matlab guess strictly, what the user wants to get. Finally the code is not slow, when you compare it with an equivalently flexible implementation in another porgramming language.
The problem of shadowing builtin functions is severe. Matlab should show a warning in such cases, and as far as I remeber this happens sometimes. I use FEX: UniqueFuncNames to check ambiguities, but this considers the toolboxes of my local Matlab installation only. When my code runs in a different Matlab version or installation, different problems can appear. But this is not specific to Matlab, but it can happen in other languages also - including the languages spoken by humen.
Summary: Matlab saves the users from shooting in their knees very well already (compare it to C :-) ) and its tries to guess smartly the users intention is sometimes not sufficient. If you want to restrict the behavior of Matlab, you cannot let Matlab guess in a "strict" mode, what it should not guess smartly, but you have to write strict code manually:
x = (3:7)';
index = [1 2 2 3 3 4];
result = reshape(x(index), size(index));
This is fast, clear and safe. Neither Matlab nor the user has to guess the intention.
An incomplete list of strict programming styles:
  • No eval or assignin
  • Specify the dimension to operate on in every case
  • Specify the parent of graphic objects
  • Use full path names instead of cd and relative paths
  • Check if fopen was successful
  • Count the output of fwrite to detect a full disk
  • Do not shadow builtin functions (controlled by an automatic tool)
  • Check each subfunction by an exhaustive unit tests including known-answer-tests and a correct detection of bad inputs (NaN, [], wrong type). Force the users to run the unit tests, when the code runs on a new Matlab version
  • Include exhaustive comments to allow for debugging and maintaining the code
  • Document all changes in a version history
  • No switch without otherwise. If a variable is defined inside an if, do this in an else block also.
  • Close files in the same function and indentation level as it is opened (means: do not open it in an IF block and close it outside of it, or the other way around)
  • Read the FAQ and Answers: dump mistakes to profit from the mistakes made by others.

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