Syntax bug R2011a: x ==y
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In coming up with an answer to another question I was playing around and think I found a bug in R2011a in Linux. Can anyone explain
>> x = randi(2, 10, 1)-1; % Dummy data
>> x == 0;
>> x ==0;
??? Error: "x" was previously used as a variable,
conflicting with its use here as the name of a function or command.
See MATLAB Programming, "How MATLAB Recognizes Function Calls That Use
Command Syntax" for details.
The 2nd and 3rd line differ in the presence (works) and absence (errors) of a space after ==. I cannot think of why the space matters. The error message also doesn't make sense to me. Is this reproducible? Is it a bug?
3 Comments
Accepted Answer
Sean de Wolski
on 20 Sep 2012
Edited: Sean de Wolski
on 20 Sep 2012
It is seeing ==0 as a string and x as a function. I.e. equivalent to:
x '==0';
This is not a bug. From the doc:
Space after an identifier, but not after a potential operator, implies a function call using command syntax. For example:
ls ./d
4 Comments
Sean de Wolski
on 20 Sep 2012
Edited: Sean de Wolski
on 20 Sep 2012
Hence it throws the error for the conflict (it wants to call x as a function but can't because it's a variable)
Also:
x('==0') is equivalent to >>x '==0' and apparently >>x ==0
Jan
on 5 Mar 2013
The different behavior between "x == 0" and "x ==0" might be a documented bug. The smartness of Matlab intelligent auto-parsing of the non-functional form exceeds the intuition of programmers. Now I'm unsure avour "x>0" and "x >=0" also.
The number of forum users struggeling with save(FileName) compared to save FileName decreases. I assume the newer documentation is better.
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