How to NOT share variable with nested function?

Hello,

I made a big code in a separate m.file, this code includes functions. I then want to make a function out of this big code, but, by doig so, i create nested functions and, as those function share the sames variable names, nothing is working properly anymore.

Is there a way to precise that the nested function inside a function should not share variables with the main function and with each other?

Thank you for your help!

[Stephen23]

@Thomas Fournier: By definition, the scope of nested functions includes all variables from their parent function/s:

https://www.mathworks.com/help/matlab/matlab_prog/nested-functions.html

https://blogs.mathworks.com/loren/2008/01/16/nested-functions-and-variable-scope/

If you need to use nested functions, then you will need to rename those variables.

But I suspect (due to that the code originally worked "in a separate m.file") that you do not need nested functions at all, and you can probably simply define them as local functions together with one main function at the start of the file, thus trivially avoiding the whole problem:

https://www.mathworks.com/help/matlab/matlab_prog/types-of-functions.html

[Thomas Fournier]

Thanks a lot it does work!

Answer 1

[Walter Roberson]

You took a script that was of the form

some code
function first
  %something
end
function second
  something
end

and you converted it to a function by putting a function line at the beginning and an end at the end of it, like

function do_stuff
some code
function first
  %something
end
function second
  something
end
end

What you should have done instead is

function do_stuff
some code
end             %end HERE, not at bottom
function first
  %something
end
function second
  something
end

[Thomas Fournier]

It works perfectly thank you!

Answer 2

[darova]

If you declare function or variable inside nested function it rewrites itself. There is no option for mistake

function main
a = 2;
b = 3;
a + b
    function nest1
    a = 5;
    a + b
    end
a + b
end

[Stephen23]

@darova: with your example the code in the nested function never runs, because you do not call the nested function. Simply placing some code after the nested function definition is not equivalent to actually calling that nested function.

Try this instead (we can also clearly see that the shared variable in the MAIN function has changed):

main()

ans = 5

ans = 8

ans = 8

function main
a = 2;
b = 3;
a + b
nest1() % <---- call the nested function!
a + b
    function nest1
    a = 5;
    a + b
    end
end

[darova]

Indeed. But why a value in main is changed?

ans = 5

ans = 8

ans = 8

I expected

ans = 5

ans = 8

ans = 5

[Walter Roberson]

The line

    a = 5;

does not make a into a local variable inside the nested function: instead it writes to the shared variable.

[Stephen23]

"But why a value in main is changed?"

Shared variables are explained in the MATLAB documentation:

https://www.mathworks.com/help/matlab/matlab_prog/nested-functions.html#f4-73993

Answer 3

[Jeff Miller]

It sounds like your "big code" is a script rather than a function, but now you want to make a function out of it.

I suggest you remove the functions from the "big code" script and put them in separate files. Then make "big code" into a function, but these other functions will no longer be nested so each will have its own separate variables.