Add an item to a class

Question

Astrik 2016-8-25

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评论： Astrik 2016-8-26

I have two classes defined: library and book. The library has name and books. Book has a name and and an author. I have a method in library class which adds book to the library. They are as follows

classdef library
    properties
        name
        books=struct('author',{},'title',{})
    end
    methods 
        function self=library(val1)
        self.name=val1;
        end
        function addbook(self,item)
            self.books(end+1)=item;
        end
    end 
 end

And the book class is

classdef book
    properties 
        author
        title
    end
    methods
        function self=book(val1,val2)
            self.author=val1;
            self.title=val2;
        end
    end    
end

Now I define

lib1=library('Leib')

and

book1=book('A','T')

When I want to add this book to my library using

lib1.addbook(book1)

I get the error

_Assignment between unlike types is not allowed.

Error in library/addbook (line 11) self.books(end+1)=item;_

Anyone can hepl me understand my mistake?

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Answer 1

Guillaume 2016-8-25

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struct and class are two completely different types even if they have the same fields/properties. You have defined the books member of your library class as an array of structures. You cannot add class objects to an array of structure. Only more structures with the same field.

The solution, is to declare your books member as an empty array of book objects:

classdef library
   properties
      name
      books = book.empty
   end
%...

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Sean de Wolski 2016-8-26

编辑：Sean de Wolski 2016-8-26

在 MATLAB Online 中打开

This is because your class is a value class not a handle class.

You can either have the library class inherit from handle (I'd recommend this!)

classdef library < handle

Or you need to passback an output from addBook.

lib = addBook(lib,book1)

The code analyzer is telling you about this with the orange underline on self above.

Astrik 2016-8-26

Exactly. It worked

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Add an item to a class

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