Why do variables that are declared as globals get set to doubles?

The variables that are declared as globals get set to doubles. This makes a consistent programming style difficult.

a.b = 3;

c(1) = a;

%   Here c is a structure, however, if you do

global d

d(1) = a;

%   You get an error stating ??? Conversion to double from struct is not possible.

Answer 1

[MathWorks Support Team]

The reason you get this error with global (or persistent) variables is that all global/persistent variables are implicitly initialized to []. Since the types need to match during subscripted assignment you get the error. In order to eliminate this error you can:

1. Avoid using the subscript (since the subscripted assignment preserves the original type)

2. Initialize d to be a struct. In this case you could use:

global d; 

if isempty(d)

       d = struct([]);

end

The basic idea behind suggestion 2 is that you need to create the variable to be a data type in the class of your choice. Then subscripted assignments into it will produce the results you'd like.