What happened to eval function?

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KAE 2022-6-15

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评论： Walter Roberson 2022-6-18

I am using R2022a, and the eval function is giving me an error,

eval(['4 + 5'])
ans = 9

Unrecognized function or variable 'eval'.

Ignore "ans = 9" in my question, since that's what happened when I ran it online in R2022a; that is the expected behavior but not what I'm getting on my computer.

Any idea what's going on? I tried restarting Matlab and the error persisted.

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dpb 2022-6-15

That's a munged install or somesuch...what doe

which -all eval

return?

eval is to be avoided unless absolutely necessary (which rarely is) but it still exists and something is amiss in the installation or path if it isn't found.

KAE 2022-6-17

>> which -all eval
built-in (C:\Program Files\MATLAB\R2022a\toolbox\matlab\lang\eval)
C:\Program Files\MATLAB\R2022a\toolbox\matlab\lang\@opaque\eval.m                         % opaque method
C:\Users\MyName\OneDrive - datacolor\matlab_programs\data processing\fdaM\@bifd\eval.m  % bifd method

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Answer 1

Walter Roberson 2022-6-16

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I think maybe you could get this error under the odd conditions:

you are inside a function
you assign to a variable named eval
you run a script
the script clears the variable named eval
after the script you try to use eval

I am not positive this will generate that exact error, but MATLAB is allowed to lose track of functions and variables if you do this or you assign to a name inside the script when the name matches a function name

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Image Analyst 2022-6-17

编辑：Image Analyst 2022-6-17

I can't imagine how it's necessary for you. Maybe if you explained the use case. It's say it's an unnecessary evil. I don't believe you EVER need to create a variable name from some string or other kind of expression. So you shouldn't need to use the evil eval.

https://matlab.fandom.com/wiki/FAQ#Why_is_it_advised_to_avoid_using_the_%22eval%22_function?

Again, what happened when you did what @dpb said:

>> which -all eval

I see

built-in (C:\Program Files\MATLAB\R2022a\toolbox\matlab\lang\eval)

C:\Program Files\MATLAB\R2022a\toolbox\matlab\lang\@opaque\eval.m % opaque method

"I pulled the whole assignment inside eval" <== that sounds like an enormous mistake. 😬

Walter Roberson 2022-6-18

I have to admit that using "syms" is very convenient, especially for creating symbolic functions or arrays of symbols. syms in that form is implemented as assignin('caller') which is a case of creating variables based upon string.

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