Defining enumerations and constants locally in MATLAB

问题

I would like to define enumerations and constants locally within the scope of a function.

I saw that MATLAB provides enumerations and constants as part of its object-oriented programming framework. However, if you try to define them within the scope of a function, they don't work. E.g. MATLAB complains with "Parse error: invalid syntax" if you try the following:

function output = my_function(input)

classdef my_constants
  properties (Constant)
    x = 0.2;
    y = 0.4;
    z = 0.5;
  end
end

classdef colors
  enumeration
    blue, red
  end
end

statements;

The reason seems to be that each classdef needs to defined in its own.m file.

I would like to avoid having an .m file for every enumeration or set of constants that I use. Is there a way to do this? What are my options?

Addendum 1:

Sine I was asked for an example, here's one in pseudocode. This example depicts my need for defining and using local enumerations.

Say I have an enumeration type called colors that can be RED or BLUE. I would like to define colors locally in my function, and use it do control the flow of my statements in the function:

function output = my_function(input)

# ....
# Code that defines the enumeration 'colors'
#....

my_color = colors;

# ... code that changes 'my_color' ...

switch my_color
   case RED
       do this
   case BLUE
       do that;

end

Addendum 2:

Could I do this by leveraging Java code? If so, how?

回答1:

I think enumerations would be overkill. You can do this by

defining a matlab struct of RGB values
determine which color is "inputted" and remembering that color fieldname

do something with that color

function output = my_function(input)

% Code that defines the enumeration 'colors' in terms of RGB

colors.RED = [1 0 0];
colors.BLUE = [0 0 1]

... etc ... 



% ... here... what determine my_color is, 
% which is logic specific to your function
% 
% You should assign 'my_color' to the same struct
% fieldname used in the above 'colors' 

if( some red conditon )

   my_color = 'RED';

elseif( some blue condition)
   my_color = 'BLUE';

elseif(etc...)

end


% at this point, my_color will be a fieldname 
% of the 'colors' struct.
% 
% You are able to dynamically extract the 
% RGB value from the 'colors' struct using 
% what is called called dynamic field reference.
%
% This means...
% 
% While you can hardcode blue like this:
%
%   colorsStruct.BLUE
%
% You are also able to dynamically get BLUE like this: 
%
%   colorName = 'BLUE';
%   rgbValue = colorsStruct.(colorName);
% 
%
% Loren has a good blog on this:
%
%   http://blogs.mathworks.com/loren/2005/12/13/use-dynamic-field-references/



% Extract the rgb value
my_color_rgb_value = colors.(my_color);


% Do something with the RGB value
your_specific_function(my_color_rgb_value);


end

Hope this helps. Please post a follow up if not.

来源：https://stackoverflow.com/questions/7931154/defining-enumerations-and-constants-locally-in-matlab

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