How to define a slicing like x(i).property in a custom class?

One minor but useful thing about image feature classes in MATLAB is that they have varieties of ways to slice the feature points and get a subset. For example, let’s say we extract SIFT features from an image:
I = imread(‘cameraman.tif’);
points = detectSIFTFeatures(I);
fprintf(‘Number of detected points: %dn’, points.Count);
We have the following ways to slice them, which give us the same sets of results:
% Subset of indices
subs = 1:10;

% Method 1
a = points(subs);
aa = a.Location;

% Method 2
b = points.Location;
bb = b(subs,:);

% Method 3
c = points.Location(subs,:);

% Method 4
d = points(subs).Location;
I’m wondering how to define a custom class to achieve all these slicing methods. I tried to use subsref function to define a custom class like this:
% File name: MyCustomPoints.m
classdef MyCustomPoints
properties
Scale % (n x 1)
Location % (n x 2)
end

methods (Access=’public’)
% Constructor
function this = MyCustomPoints(scale, location)
this.Scale = scale;
this.Location = location;
end
% Slicing
function varargout = subsref(this, s)
switch s(1).type
case ‘()’
subs = s(1).subs{1};
varargout{1} = MyCustomPoints(this.Scale(subs,:), …
this.Location(subs,:));
case ‘.’
% Handle property access
if isscalar(s)
varargout{1} = this.(s(1).subs);
else
[varargout{1:nargout}] = builtin(‘subsref’, this, s);
end
end
end
end
end
Below is an example usage of this class:
% Example input
Scale = rand(100,1);
Location = rand(100,2);
myPoints = MyCustomPoints(Scale, Location);
subs = 1:3; % subset indices

% Method 1
a = myPoints(subs);
aa = a.Location; % –> Successful.

% Method 2
b = myPoints.Location;
bb = b(subs,:); % –> Successful.

% Method 3
c = myPoints.Location(subs,:); % –> Successful.

% Method 4
d = myPoints(subs).Location; % –> Failed.
Only the last slicing method gives me an error message:
Output argument "varargout{2}" (and possibly others) not assigned a value
in the execution with "MyCustomPoints/subsref" function.
Could you please advise how to modify my class to enable all the slicing methods above?One minor but useful thing about image feature classes in MATLAB is that they have varieties of ways to slice the feature points and get a subset. For example, let’s say we extract SIFT features from an image:
I = imread(‘cameraman.tif’);
points = detectSIFTFeatures(I);
fprintf(‘Number of detected points: %dn’, points.Count);
We have the following ways to slice them, which give us the same sets of results:
% Subset of indices
subs = 1:10;

% Method 1
a = points(subs);
aa = a.Location;

% Method 2
b = points.Location;
bb = b(subs,:);

% Method 3
c = points.Location(subs,:);

% Method 1
a = myPoints(subs);
aa = a.Location; % –> Successful.

% Method 2
b = myPoints.Location;
bb = b(subs,:); % –> Successful.

% Method 3
c = myPoints.Location(subs,:); % –> Successful.

% Method 4
d = myPoints(subs).Location; % –> Failed.
Only the last slicing method gives me an error message:
Output argument "varargout{2}" (and possibly others) not assigned a value
in the execution with "MyCustomPoints/subsref" function.
Could you please advise how to modify my class to enable all the slicing methods above? One minor but useful thing about image feature classes in MATLAB is that they have varieties of ways to slice the feature points and get a subset. For example, let’s say we extract SIFT features from an image:
I = imread(‘cameraman.tif’);
points = detectSIFTFeatures(I);
fprintf(‘Number of detected points: %dn’, points.Count);
We have the following ways to slice them, which give us the same sets of results:
% Subset of indices
subs = 1:10;

% Method 1
a = points(subs);
aa = a.Location;

% Method 2
b = points.Location;
bb = b(subs,:);

% Method 3
c = points.Location(subs,:);

% Method 1
a = myPoints(subs);
aa = a.Location; % –> Successful.

% Method 2
b = myPoints.Location;
bb = b(subs,:); % –> Successful.

% Method 3
c = myPoints.Location(subs,:); % –> Successful.

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