How to define a constant using another one in a Matlab class

Question

I can't figure out how to do such a simple thing like defining constants using other ones.

For instance, a dummy example :

classdef DummyClass < handle
    properties (Constant)
        NB_SECONDS_IN_MINUTE = 60;
        NB_MINUTES_IN_HOUR   = 60;

        NB_SECONDS_IN_HOUR   = NB_SECONDS_IN_MINUTE * NB_MINUTES_IN_HOUR;
    end
end

This does not work :(

I then tried with this line :

NB_SECONDS_IN_HOUR   = DummyClass.NB_SECONDS_IN_MINUTE * DummyClass.NB_MINUTES_IN_HOUR;

but that doesn't work either...

Someone got a clue here ? :/

(I'm using MATLAB R2009a btw)

it said "undefined variable or class DummyClass". btw, Edric gave me the solution : i just forgot that my class was in a subfolder, and in Matlab, one needs to use the fully qualified name of a class (including sub-directories) — adrien.pain
– adrien.pain, Commented Jan 26, 2012 at 16:31

Edric · Accepted Answer · 2012-01-26 15:08:46Z

7

You definitely need to refer to the constants with the full class name, as in your second case. Is DummyClass within a package (+packagename) directory? If so, you need to use the fully qualified name, i.e.

NB_SECONDS_IN_HOUR = packagename.DummyClass.NB_SECONDS_IN_MINUTE * packagename.DummyClass.NB_SECONDS_IN_HOUR;

EDIT: just tested this in R2009a:

>> ver matlab
-------------------------------------------------------------------------------------
[...]
-------------------------------------------------------------------------------------
MATLAB                                                Version 7.8        (R2009a)
>> type DummyClass

classdef DummyClass < handle
    properties (Constant)
        NB_SECONDS_IN_MINUTE = 60;
        NB_MINUTES_IN_HOUR   = 60;

        NB_SECONDS_IN_HOUR   = DummyClass.NB_SECONDS_IN_MINUTE * DummyClass.NB_MINUTES_IN_HOUR;
    end
end

>> DummyClass.NB_SECONDS_IN_HOUR
ans =
        3600

answered Jan 26, 2012 at 15:08

Edric

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2 Comments

Alexxx Over a year ago

So it depends on the path where we code the class??? (and so we can't reuse this class directly in anoter project without the same directories structure?)

Edric Over a year ago

It only matters if you place DummyClass.m in a MATLAB package directory, i.e. one beginning with "+". When you do that, you alter the fully-qualified name of the class.

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