Object indexed references are in three forms — parentheses, braces, and dot-name:
A(I)
A{I}
A.name
Each of these statements results in a call by MATLAB® to the subsref of class A, or
a call to the built-in subsref function if the class of
A does not implement a subsref method.
MATLAB passes two arguments to subsref and requires subsref to return the result of the indexed reference:
B = subsref(A,S)
The first argument is the object being referenced, A. The second argument, S, is a substruct with two fields:
S.type is a char vector containing '()', '{}', or '.' specifying the indexing type used.
S.subs is a cell array or char vector containing the actual index or name. A colon used as an index is passed in the cell array as the colon character ':'. Ranges specified using a colon (e.g., 2:5) are expanded to 2 3 4 5.
For example, the expression:
A(1:4,:)
Causes MATLAB to call subsref(A,S), where S is a 1-by-1 structure with a two-element cell array. The cell array contains the numbers 1, 2, 3, 4, and the colon character :.
S.type = '()' S.subs = {1:4,':'}
Returning the contents of each cell of S.subs gives the index values for the first dimension and a char vector ':' for the second dimension:
S.subs{:}
ans =
1 2 3 4
ans =
:The default subsref returns all array elements in rows 1 through 4 and all the columns in the array.
Similarly, this expression:
A{1:4}
Uses a cell array containing the numbers 1, 2, 3, 4.
S.type ='{}'
S.subs = {1:4} The default subsref returns the contents of all cell array elements in rows 1 through 4 and all the columns in the array.
This expression:
A.Name
Calls subsref(A,S), where the struct
S has these values:
S.type = '.' S.subs = 'Name'
These simple calls are combined for more complicated indexing expressions. In such cases, length(S) is the number of indexing levels. For example,
A(1,2).PropertyName(1:4)
calls subsref(A,S), where S is a 3-by-1 array of structs with the values:
S(1).type = '()' S(2).type = '.' S(3).type = '()' S(1).subs = {1,2} S(2).subs = 'PropertyName' S(3).subs = {1:4}