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Is there something like a 'struct pointer' in Matlab?

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Yingzhi on 28 Aug 2012
Let's assume that I have a pretty deep structure called dataPool and I'm currently at level 'dataPool.instrument.profile.experiment'. Every time I want to change something I have to write ' = ...;'. My question is, can I somehow make a reference to it, let's call it 'exp', so that 'exp' delegates all the changes for 'dataPool.instrument.profile.experiment' ?
If I simply write 'exp = dataPool.instrument.profile.experiment;', everything is copied by value, which means when I write 'exp.inputChannel = blahBlah', a new field 'inputChannel' would be created for 'exp' instead of 'dataPool.instrument.profile.experiment'.
Could some one help me on this? Thanks!

Accepted Answer

Daniel Shub
Daniel Shub on 29 Aug 2012
I disagree with Walter and think MATLAB does provide this functionality in the OO HANDLE superclass. You can create a handle structure class
classdef hstruct < handle
function obj = hstruct(data) = data;
Then if you can do
>> a.b.c = hstruct(1);
>> d = a.b.c;
>> = 2;
ans =

More Answers (3)

Jan on 28 Aug 2012
Edited: Jan on 28 Aug 2012
No, exp = dataPool.instrument.profile.experiment does not make a deep data copy, but the fields of exp are shared data copies. Then this adds two new fields:
exp.fieldA = 1:100;
exp.fieldB.fieldB1 = rand(100);
Then the temporary exp is copied back again:
dataPool.instrument.profile.experiment = exp;
This creates again shared data copied, such that the memory for the data is not duplicated. In some usual test scenarios this is faster than:
% Slower:
dataPool.instrument.profile.experiment.fieldA = 1:100;
dataPool.instrument.profile.experiment.fieldB.fieldB1 = rand(100);
The overhead for addressing the substructs causes the delay. But the timings can and will depend on the Matlab version and most likely the number of fields and the depth of the nested structure. Because the field addressing does not require a lot of time, the differences in the timings are small and the example "rand(100)" will be more expensive. But when exp contains large data already, the shared data copy method help to reduce the processing time.
James Tursa
James Tursa on 28 Aug 2012
FYI, regarding C-mex routines, it is not always possible to even tell when a field element (or cell element) is shared with another variable via a shared parent. MATLAB provides no functions in the API to tell you, and hacking into the variable itself doesn't always tell you either.

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Darik on 28 Aug 2012
This is probably a bad idea but maybe it could come in handy in some situations:
dataPool = dynamicprops;
dataPool.instrument = dynamicprops;
dataPool.instrument.profile = dynamicprops;
dataPool.instrument.profile.experiment = dynamicprops;
exp = dataPool.instrument.profile.experiment;
exp.inputChannel = 8;
>> dataPool.instrument.profile.experiment.inputChannel
ans =

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