| structure arguments sometimes behave like value types - why? [message #53606] |
Fri, 20 April 2007 13:10 |
justspam03
Messages: 36
Registered: October 2003
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Member |
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Hi all,
according to the IDL reference, structures (as a whole) are treated
like reference types when supplied as an argument. A small test
program of the kind
pro main
ns = { nullableString, hasValue: 0, value: '' }
a = { nullableString }
a.value = '3'
changeval, a
print, a.value
end
pro changeval, s
s.value = '4'
end
confirms this - after the call to changeval, a.value has value '4'.
However, when the structure is an object variable as in the example
appended below, it seems that only a copy of structtest.val is
exchanged, not a reference to it. The final call to printValue in
'main' prints a '1'.
Could someone please explain why? What am I missing?
Thanks a lot
Oliver
pro main
ns = { nullableString, hasValue: 0, value: '' }
x = obj_new('structtest') ; object contains membervariable of type
nullableString
x->set, '1' ; set value of nullableString to '1'
x->printValue ; and print
b = x->getStruct() ; get reference? value?
b.value = '2'
x->printValue ; result is still '1' ! Why?
end
function structtest::init
return, 1
end
pro structtest::set, value
self.val.value = value
end
pro structtest::printValue
print, self.val.value
end
function structtest::getStruct
return, self.val
end
pro structtest__define
obj = { STRUCTTEST , val: {nullableString} }
end
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