Method with struct input: how to accept different object subfields?
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Hi all,
In a method, how to accept different object subfields?
https://uk.mathworks.com/help/matlab/matlab_oop/ordinary-methods.html
Above site gives an example of addData method. Code is here:
classdef MyData
properties
Data = 0
end
methods
function obj = addData(obj,val)
newData = obj.Data + val;
obj.Data = newData;
end
end
end
My understanding is when applying addData to object, 'val' can be replaced with any variable to allow different inputs, which is good.
However, if there is another output subfield in obj, say 'Data1', this method cannot be reused to 'Data1', as it will only recognize 'Data' as the subfield here.
Of course I can write a new method:
function obj = addData1(obj,val)
newData = obj.Data1 + val;
obj.Data1 = newData;
end
such that Data1 can also be accepted, but this is cumbersome as the operation is repeated. What is the correct way to allow different struct function output here?
Thank you!
1 个评论
Numbering variables is a bad design decision which makes code more complicated, slower, and buggier:
采纳的回答
I'm not sure I understand fully what you're asking, particularly as you're not using correct terms. There are no structures, fields or subfields in any of the code you've shown (and I've no idea what you mean by output subfield). An object has properties (and methods, and optionally events).
The properties of an objects are defined in the classdef block. While there is a way to have dynamic properties in matlab it's a fairly advanced form of programming which I wouldn't recommend. For the common case the properties are set by the class and the user of the class cannot create more properties.
Also note that in the example you've shown the addData method is not particularly useful since the property is public (i.e. can be modified by users of the class). You could simply bypass it and do:
o = myData; %instantiate object
o.Data = o.Data + val; %modify Data directly without calling addData
I'm not sure what it is you're trying to do. What is your ultimate goal?
10 个评论
Xh Du
2017-3-10
Guillaume
2017-3-10
One possible option:
classdef MyData
properties
Data = 0;
Data1 = 0;
end
methods
function obj = addData(obj, propname, value)
assert(isprop(obj, propname), '%s is not a property of the object', propname);
obj.(propname) = obj.(propname) + value;
end
end
end
Which you would then use with:
o = MyData;
o = o.addData('Data', 5);
o = o.addData('Data1', 10);
But as I've already pointed out, you can replace the three lines above by:
o = MyData;
o.Data = o.Data + 5;
o.Data1 = o.Data1+ 10;
which is much simpler and doesn't need the addData method.
Xh Du
2017-3-10
If you are applying the same thing to lots of properties why aren't you just storing them in an array? It sounds like a problem of design before you get to your class if you are needing to do this on any major scale.
Classes do not work well as a way to keep changing lots of properties lots of times. My current algorithm is running excessively slowly because of a lot of property accessing so I will either have to reprogram it to access the properties fewer times or simply remove the class part of it altogether and work on the rawest form of the data I can.
Xh Du
2017-3-10
Guillaume
2017-3-10
As Adam said, all your problems come from bad design. A simple rule: if you're numbering variables, your design is wrong. These numbered variables should be replaced by a matrix/cell array/similar container.
In your case:
classdef myproj < handle %you seem to have switched to handle class but still use value class syntax for your method
properties
container = cell(2, 3);
test
end
methods
function this = myproj(a1, a2, a3, b1, b2, b3) %and even here accepting a cell array would be simpler
%class constructor
this.container = {a1, a2, a3; b1, b2, b3};
end
function testcase(this, aorb) %handle syntax
row = ismember(aorb, {'a', 'b'})
this.test = this.container{row, 1) .^ 2 + ...
this.container{row, 2) * sum(this.container{row, 1}(:) - ...
this.container{row, 1} / norm(this.container{row, 3}, 'fro');
end
end
end
Xh Du
2017-3-10
Adam
2017-3-10
[~,row] = ismember(aorb, {'a', 'b'})
Guillaume
2017-3-10
Yes, slight bug, but you get the idea. Note that in real code, I wouldn't use char arrays as toggles, I would either pass the numeric index of the row directly or use categoricals.
Xh Du
2017-3-13
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