Accessing member via set's NON-const iterator that doesn't affect invariants
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29-06-2021 - |
题
Let's say I have code like so:
#include <set>
#include <math.h>
typedef int OtherTypes;
struct MyType
{
double Field1;
OtherTypes MoreFields;
MyType(double blah) :
Field1(blah)
{
}
bool operator < (const MyType &That) const
{
// Does not use any other member besides Field1
return ( fabs(Field1 - That.Field1) > 1e-6 &&
Field1 < That.Field1 );
}
};
int main()
{
std::set<MyType> foo;
std::pair< std::set<MyType>::iterator,
bool > inchk = foo.insert(MyType(1.0));
OtherTypes SomeVal = 1;
if ( inchk.second )
inchk.first->MoreFields = SomeVal; // error
}
How do I reassure the compiler that writing MoreFields will not affect any invariants or will not do anything to invalidate the order of elements in the set?
If the only recourse is to use another container such as vector, how do I insert a new value in the sorted position while checking if one exists already?
解决方案
Declare
MoreFields
asmutable
, orconst_cast
theinchk.first
expression to remove constness, orencapsulate
MoreFields
within a const-qualified accessor that returns a non-const reference.
其他提示
I would think you want to use a map instead of a set.
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