"I just want cr to be "part of" M"   I don't understand what you try to say. I read it as " M has a cr", but your code says " cr is-a M". Anyhow, try
M = mesh1D( [0 1], 10 );
M = M.generate;
cr = crack( [0 1], 10, [0.13,0.75] );
cr = cr.generate;
and
>> cr
cr =
crack with properties:
place: [0.1300 0.7500]
domain: [0 1]
nElem: 10
nNode: 11
node: [11x2 double]
element: [10x3 double]
connectElemNode: []
where
classdef mesh1D
properties
domain = [0 1];
nElem = 10;
nNode = 11;
node;
element;
connectElemNode;
end
methods
function obj = mesh1D(domain, nElem)
obj.domain = domain;
obj.nElem = nElem;
end
function obj = generate(obj)
a = obj.domain(1);
b = obj.domain(2);
gridSize = (b-a)/obj.nElem;
obj.node = [(1:obj.nElem+1)' (a:gridSize:b)'];
obj.element = [(1:obj.nElem)' (1:obj.nElem)' (2:obj.nElem+1)'];
end
end
end
and
classdef crack < mesh1D
properties
place
end
methods
function obj = crack(varargin)
obj = obj@mesh1D(varargin{1:2});
obj.place = varargin{3};
end
end
end
 
Notes:
- M and cr are value classes. See Comparison of Handle and Value Classes
- "I do not understand why I have to call the superclass"   because that's the way Matlab OOP is designed. The object cr doesn't know anything about the object M
- "as if cr would be a structure within the M structure in functional programming"   this is rather a description of a M has-a crack relationship
 
has-a: try
cr = crack( [0.13,0.75] );
M = mesh1D( [0 1], 10, cr );
M = M.generate;
where
classdef mesh1D
properties
domain = [0 1];
nElem = 10;
nNode = 11;
node;
element;
connectElemNode;
crack
end
methods
function obj = mesh1D(domain, nElem, crk )
obj.domain = domain;
obj.nElem = nElem;
obj.crack = crk;
end
function obj = generate(obj)
a = obj.domain(1);
b = obj.domain(2);
gridSize = (b-a)/obj.nElem;
obj.node = [(1:obj.nElem+1)' (a:gridSize:b)'];
obj.element = [(1:obj.nElem)' (1:obj.nElem)' (2:obj.nElem+1)'];
end
end
end
and
classdef crack
properties
place
end
methods
function obj = crack(plc)
obj.place = plc;
end
end
end
