Refer to Enumerations

Instances of Enumeration Classes

Enumeration members are instances of the enumeration class. You can assign enumeration members to variables and form arrays of enumeration members. If an enumeration class derives from a superclass, you can substitute an enumeration member for an instance of the superclass.

The WeekDays class defines enumeration members for five days of the week.

classdef WeekDays
   enumeration
      Monday, Tuesday, Wednesday, Thursday, Friday
   end
end

Create objects of the WeekDays class representing specific days.

today = WeekDays.Monday;
tomorrow = WeekDays.Tuesday;

The variables today and tomorrow are objects of the WeekDays class.

The PPM class defines three enumeration members. Each member has an associated numeric value derived from the class superclass.

classdef PPM < double
   enumeration
      High (1000)
      Medium (100)
      Low (10)
   end
end

Assign an enumeration member to a variable.

level = PPM.High;

When you substitute enumeration members for instances of the superclass, MATLAB® coerces the enumeration member to the superclass. For example, add a numeric value to an enumeration member of the PPM class.

levelNew = level + 100

levelNew =

        1100

The result is of class double.

whos
  Name          Size            Bytes  Class    Attributes

  level         1x1               108  PPM                
  levelNew      1x1                 8  double

You can substitute superclass values for corresponding enumeration members. For example, pass one of the numeric values defined in the enumeration class to the PPMSwitch function. 

function PPMSwitch(ppm)
   switch ppm
      case PPM.Low
         disp Low
      case PPM.Medium
         disp Medium
      case PPM.High
         disp High
   end
end
PPMSwitch(100)
Medium

You can also use an enumeration member directly:

PPMSwitch(PPM.Medium)
Medium

For information on operations you can perform on enumeration class instances, see Operations on Enumerations.

Conversion of Characters to Enumerations

Enumeration classes can convert char vectors to enumeration members when the char vector represents an enumeration member defined by the class. This conversion enables you to pass a valid char vector or a cell array of char vectors when enumerations are expected.

Use a char vector instead of a direct reference to an enumeration member when you want to use a simple character string to specify an enumeration member. However, specifying an enumeration member directly eliminates the conversion from char to enumeration.

Enumeration classes provide a converter function using the constructor syntax.

today = WeekDays('Tuesday');

Because the char vector 'Tuesday' matches the enumeration member WeekDays.Tuesday, the Weekdays char method can perform the conversion.

class(today)
ans =

WeekDays

Create an enumeration array using the WeekDay class constructor and a cell array of char vectors.

wd = WeekDays({'Monday','Wednesday','Friday'})
wd = 

    Monday       Wednesday    Friday 
class(wd)
ans =

WeekDays

All char vectors in the cell array must correspond to an enumeration member defined by the class.

Coercion of char to Enumerations

MATLAB coerces char vectors into enumeration members when the dominant argument is an enumeration. Because user-defined classes are dominant over the char class, MATLAB attempts to convert the char vector to a member of the enumeration class.

Create an enumeration array. Then insert a char vector that represents an enumeration member into the array.

a = [WeekDays.Monday,WeekDays.Wednesday,WeekDays.Friday]
a = 

    Monday       Wednesday    Friday

Add a char vector to the WeekDays array.

a(end+1) = 'Tuesday'
a = 

    Monday       Wednesday    Friday       Tuesday

MATLAB coerces the char vector to a WeekDays enumeration member.

class(a)
ans =

WeekDays

Substitute Enumeration Members for char Vectors

You can use enumeration members in place of char vectors in cases where functions require char vectors. For example, this call to sprintf expects a char vector, designated by the %s format specifier.

sprintf('Today is %s',WeekDays.Friday)
ans =

Today is Friday

The automatic conversion of enumeration classes to char enable you to use enumeration members in this case.

Enumeration Arrays

Create enumeration arrays by:

  • Concatenating enumeration members using []

  • Assigning enumeration members to an array using indexed assignment

Create an enumeration array of class WeekDays by concatenating enumeration members:

wd = [WeekDays.Tuesday,WeekDays.Wednesday,WeekDays.Friday];

Create an enumeration array of class WeekDays by indexed assignment:

a(1) = WeekDays.Tuesday;
a(2) = WeekDays.Wednesday;
a(3) = WeekDays.Friday;

Mixed Enumeration Members and char Vectors

You can concatenate enumeration members and char vectors as long as the char vector represents an enumeration member. 

clear a
a = [WeekDays.Wednesday,'Friday'];
class(a)
ans =

WeekDays

You can also assign a char vector to an enumeration array:

clear a
a(1) = WeekDays.Wednesday;
a(2) = 'Friday';
class(a)
ans =

WeekDays

Default Enumeration Member

The default member of an enumeration class is the first enumeration member defined in the enumeration block. For the WeekDays class, the default enumeration member is WeekDays.Monday.

classdef WeekDays
   enumeration
      Monday, Tuesday, Wednesday, Thursday, Friday
   end
end

MATLAB allows assignment to any element of an array, even if the array variable does not previously exist. To fill in unassigned array elements, MATLAB uses the default enumeration member.

For example, assign a value to element 5 of an array, a:

clear a
a(5) = WeekDays.Tuesday;

MATLAB must initialize the values of array elements a(1:4) with the default enumeration member. The result of the assignment to the fifth element of the array a is:

a
a = 

    Monday       Monday       Monday       Monday       Tuesday

See Also

Topics