Array of derived-class objects: Catch-22?

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David Goldsmith 2011-7-20

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https://ww2.mathworks.cn/matlabcentral/answers/12040-array-of-derived-class-objects-catch-22

Hi! I'm trying to write an "intelligent" array extender--one that presents a single interface to extend numeric, character, cell, structure, and object arrays. I've succeeded w/ the first four, but am stuck on the last because the syntax I'm trying to use:

a(n+i).(prop) = item(i).(prop)

calls a's constructor w/ no arguments, so its c-tor has to handle the no argument case. However, if I do so as described in the help documentation, i.e., by encasing the body of the c-tor in an if nargin~=0 block, apparently I can't combine this w/ a derived class that calls its superclass c-tor, 'cause I get the error:

A constructor call to superclass <superclass name> is not a top-level statement.

(And if I try to get around this by relegating the if block to the superclass' c-tor, then the derived class' c-tor complains when the array builder calls its c-tor.)

Bug or "feature"? Workaround? Thanks!

OlyDLG

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Answer 1

David Goldsmith 2011-7-20

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https://ww2.mathworks.cn/matlabcentral/answers/12040-array-of-derived-class-objects-catch-22#answer_16491

OK, I think I found the answer (I guess it only makes sense that the more complicated my code becomes, the more of the help doc I'm going to have to read...): I have to provide default values for all my derived-class' properties in the properties def. section and then, in the no arguments case, provide default values for the superclass' c-tor arguments (if it doesn't also handle the no arguments case). I'll test this and reply if it doesn't work.