Not enough input arguments, when inputs are specified

Question

This feels like a really dumb question because the error message is really straight forward, so I took a while to create as simple of a complete example as I could. It seems like when a constructor is called in a constructor ( I think I first noticed in a normal method not a constructor) and the objects are being put into an array in reverse order then matlab will give a not enough input arguments error for example:

classdef practice
    methods
        function self = practice(b)
            b
            if b>1
                for i = 2:-1:1
                    s(i) = practice(b-i);
                end
            end
        end
    end
end

called as

practice(4)

gives

b =

     4


b =

     2


b =

     0

Error using practice (line 4)
Not enough input arguments.

Error in practice (line 7)
                    s(i) = practice(b-i);

Error in practice (line 7)
                    s(i) = practice(b-i);

This case is odd because it only fails when getting to where b <= 1, but my real code doesn't fail like this. Any ideas on what exactly is going wrong and how I can fix it?

Actually the constructor can't have an instance as the first method, but isn't static. — Hovestar
– Hovestar, Commented Jul 17, 2015 at 19:32

JustinBlaber · Accepted Answer · 2015-07-17 19:03:21Z

1

I think the problem is on the first iteration, when b = 4, you set s(i) = practice(b-i) and i = 2. This will initialize s to an array of practice of length 2, but since you initialize the second element first, the first element will get initialized to a default practice, where input b is undefined.

If you change the indices over i iterates to i = 1:2 this should fix the problem.

Edit:

For example, try clearing your workspace and then doing:

s(2) = practice(0)

This will attempt to assign practice(0) to s(2) and then s(1) will get assigned a default initialized practice, in which case b is not defined. This will replicate the problem you're having. The solution is to assign to s(1) first, and then s(2) next.

edited Jul 17, 2015 at 19:03

answered Jul 17, 2015 at 18:53

JustinBlaber

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