Possible to create a function where the input is changed?

I understand it is one of the "cardinal rules" of MATLAB that functions do not affect the input values (versus scripts that do); however, is it possible to create a function where this is violated?

For example:

>>x = 10

>>Function(x)

%Running this would change the value of x in the workspace to some other value

Answer 1

[Sean de Wolski]

doc assignin
doc evalin

Why would you want to do this?

[Josh]

How would I use these if I wanted to, say, increase the value of x from 1 to 2?

It's more conceptual. To be honest, you could say I made a bet with someone.

[Sean de Wolski]

Read the documentation I linked to. I'll only give you more details if you cut me in on your winnings!

[Josh]

Oh, that's the command for documentation. I'll be sure to check it out, thanks!

[Walter Roberson]

If the bet is just whether it can be done or not, then the answer is Yes, it can. If the question is whether _you_ can come up with a way to do it, then us telling you the mechanism would probably violate the terms of the bet.

We'd _prefer_ not to describe the details. The question is sort of like asking a professional electrician about using coins to replace fuses: the answer is going to be, "Don't Do That!"

[Josh]

It was more a bet of whether or not you can or cannot do it. I'll be sure to try and figure it out using that documentation; worst case scenario I'll use Matt's idea.

[Josh]

Was able to create a function to do just this using assignin, thank you!

Answer 2

[Matt Tearle]

I am not doing this...

classdef passbyref < handle

      properties
          value
      end

      methods
          function x = passbyref(y)
              x.value = y;
          end
          function notagreatidea(x)
              x.value = x.value + 1;
          end
      end

end

And then

>> x = passbyref(42)
>> notagreatidea(x)
>> x

May Cleve have mercy on my soul.

Also: what Sean and Walter said.

[Josh]

Is this all one function? (excluding the three lines at the bottom)

[Sean de Wolski]

Nope there are two functions and a class definition in there.

[Walter Roberson]

A class definition is not considered a function.

classdef need to go in to .m files with the same name as the class being defined, and "classdef" must be the first non-blank non-comment line, and nothing except whitespace and comments can go after the "end" of the classdef.

[Josh]

I should have been more specific: should this all be in one file, or must I create seperate files for passbyref and notagreatidea?

[Sean de Wolski]

no, you need just one file. You could ghave multiple files (for the methods) but then you'd need a special folder - not worth it for two one-line methods.

http://www.mathworks.com/help/techdoc/matlab_oop/ug_intropage.html

[Matt Tearle]

I'll let you argue the semantics with your bet opponent, but notagreatidea is kindasorta a function -- it's actually a method of the passbyref class. So it only works on passbyref objects. However, once you have a passbyref object (x = passbyref(42)), it is a single "function call" that invokes the notagreatidea method and changes its value property.

For the sake of your bet, follow Sean's first link... [hint]

[Josh]

Thanks for the help, but went with Sean's answer for simplicity's sake.

Answer 3

[Walter Roberson]

Yes, it is possible. There are not many cases where it is a good idea, however.