Overload end for Classes - MATLAB & Simulink (original) (raw)

Main Content

In a standard MATLAB® indexing expression, end returns the index value of the last element in the dimension in whichend appears. For example, in A(4,end), theend method returns the index of the last element in the second dimension of A. You can overload end in classes for specialized behavior.

Syntax and Default Behavior

This is the syntax MATLAB uses to call the end method.

• A is the object being indexed into.
• k is the dimension in the indexing expression whereend appears.
• n is the total number of indices in the expression.
• ind is the index value to use in the expression.

Note

You cannot call the end method directly using this syntax. MATLAB automatically calls the method when it encounters end in an indexing expression.

For example, A is a 2-by-3 array of doubles. When MATLAB encounters the expression A(end,1), it calls theend method with these arguments.

• A is the object.
• k = 1 because end appears in the first dimension of the indexing expression.
• n = 2 because the expression has two indices.

The end method returns 2, which is the index of the last element in the first dimension of A.

How RedefinesParen Overloads end

Any overload of the end method must have the calling syntaxind = end(A,k,n). For example, the modular indexing class matlab.mixin.indexing.RedefinesParen has a built-in overload ofend.

function ind = end(obj,k,n) sz = size(obj); if k < n ind = sz(k); else ind = prod(sz(k:end)); end end

Theif-else statement calculates the return value based on where theend appears in the indexing expression and whether the indexing expression has values for all of the dimensions of the object array. For example, whenB is a 2-by-3-by-2 object array of a type that inherits fromRedefinesParen:

• k < n: When end is not the last value in the indexing expression, the overload returns the last value in that dimension. For B(1,end,4), end returns the size of the second dimension, 3.
• k = n: When end is the last element in the indexing expression, the overload handles two cases:
  • If the indexing expression references all the indices, thenprod(sz(k:end)) gives the same result assz(k). For example, inB(1,2,end), end returns2.
  • If the indexing expression does not reference all the indices, thenprod(sz(k:end)) returns the product of the size of dimension k and the sizes of all unreferenced dimensions. For example, in B(1,end),end returns the product of the sizes of the second and third dimensions, 6.

RedefinesParen defines size as an abstract method for the class author to implement, so the two methods are dependent on one another for the final behavior. See the Customize Parentheses Indexing example for a class that implements a size method that provides the expectedend behavior with an array.

See Also

Topics

• Objects in Index Expressions