Using structures as enum input to a function in MATLAB

Hello

I'm implementing a function that gets as one input with two possible values Red (enum configured as 1) , Green(enum configured as 2).

so what I did in matlab is this:

colors = struct('Red', 1, 'Green', 2);
function output=choose(colors)
{
if (colors == Red) %in other words if I input 'Red' to function choose
 do something
else (colors == Green )%in other words if input is 'Green' to function choose
 do something
}

So I want to write this, choose (Red) or choose(Green) and get the required output of a function. this means I want to write in my editor after building the function just this : choose(Red) or choose (Green) then I get output.

How I can implement that in matlab? as I showed above it tells me once I write choose(Red) that Red isn't defined although I already defined it as structure above the function... any help?!

Answer 1

[Jan]

You have defined a struct, but this is not an enum. With your code (if you omit the curly braces), you could use:

 choose(colors.Red) 

becaus your have created a struct. Matlab cannot guess, that you want to treat the field names for another purpose.

You need to defined an enumeration class for an enumeration: doc enumeration

Even then you need to sepcify the enumeration class in addition and choose(Red) is not possible:

 classdef colors
   enumeration
      Red, Green
   end
 end
 
 choose(colors.Red) 

[Jimmy cho]

I understand and thanks for your reply, but lets assume I want to call the function choose, as how?

I mean lets assume Im on the other function and I want to call choose function, so I cant write choose(Red) ? so how do I understand what the user input to choose function?

my probelm is that: the user has to input to the function choose Red or Green as input , it means to write choose(Red) or to write choose(Green) so how do I do that in matlab? isn't possible? don't guess so.

[Jimmy cho]

@jan and where do I write classdef colors inside the function choose or in the upper/above of the function body? thanks.

[Jan]

The class must be defined where all functions, which use it, can see it, e.g. in a folder in Matlab's path.

Why is it needed to call exactly "choose(Red)"? Of course, you can define a variables called "Red", which contains e.g. the string 'red'. But then you have to do this in every function in the same way and this is a fragile approach.

Remember, that using more colors as names directly will collide with the built-in commands pink, gray, copper. Only the upper/lowercase would help then. Using color.red is smarter and clearer.

[Jimmy cho]

I need to define it as Red or Green (1 or 2 ) because the input parameter that I input to my function is either

Red or Green (corresponded to 1 or 2 integer numbers )

[Jimmy cho]

So how do I define above evey function the Red or Green enum/definition?

[Jan]

@Jimmy cho: I strongly recommend not to do that and I do not believe that this is a clean programming style, but it works easily:

Insert in each function, which uses the variables, these lines:

Red   = 1;
Green = 2;

Alternatively create a script, which contains these lines und call it from each function before the variables are used. Then you have to change only one code, if you add a new color. Remember, that this can slow down the processing massively, because the JIT-accelerator might not know the type of the concerned variables. Therefore I'd never use a script for anything.

The clean way is to define an enumeration class and "color.red" instead of "Red". I cannot imagine, why this clean and efficient method does not satisfy your needs and why choose(Red) is so much better then e.g. choose('red') .

[per isakson]

Why not

 classdef colors < uint8
   enumeration
      Red    (1)
      Green  (2)
   end
 end