Re: [ quantlib-Bugs-3307791 ] g++ complains about mutable variables

Posted by Amir Ahmed Ansari-2 on Jun 22, 2011; 9:23am
URL: http://quantlib.414.s1.nabble.com/quantlib-Bugs-3307791-g-complains-about-mutable-variables-tp8832p8833.html

I haven't looked at the code responsible for this, but for anyone wishing to resolve it, here is one tidbit that may be useful. The mutable C++ keyword is not meaningful on reference member variables. That is because the 'const' keyword applies ONLY to the class members, NOT what they might be pointing to. So, the following will execute without any compiler errors:

class A
{
public:

    mutable int & i;
    int a;

    A() : i(a) {}

};

int main()
{
    const A a;
    a.i = 1;

     return 0;

}

NOTE that this isn't an example you should copy, because changing those members of a const object that are not marked 'mutable' can lead to very subtle bugs. What I am trying to explain is that the mutable keyword is irrelevant on class members that are references. Hope this helps!!!!

----- Original Message -----
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Sent: Tuesday, June 21, 2011 10:07 PM
Subject: [Quantlib-dev] [ quantlib-Bugs-3307791 ] g++ complains about mutable variables

Bugs item #3307791, was opened at 2011-05-26 03:07
Message generated for change (Comment added) made by fak98
You can respond by visiting:
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Category: None
Group: None
Status: Open
Resolution: None
Priority: 5
Private: No
Submitted By: charas (benyam)
Assigned to: Nobody/Anonymous (nobody)
Summary: g++ complains about mutable variables

Initial Comment:
While building a package for quantlib on  archlinux i got the following warning and error 

reference 'y2_' cannot be declared 'mutable' [-fpermissive]
../ql/math/interpolations/multicubicspline.hpp:277:34: warning: reference 'v_' cannot be declared 'mutable' [-fpermissive]
../ql/math/interpolations/multicubicspline.hpp:336:33: warning: reference 'y2_' cannot be declared 'mutable' [-fpermissive]
../ql/math/interpolations/multicubicspline.hpp:337:34: warning: reference 'v_' cannot be declared 'mutable' [-fpermissive]
../ql/math/interpolations/multicubicspline.hpp:337:39: warning: reference 'v1_' cannot be declared 'mutable' [-fpermissive]
../ql/math/interpolations/multicubicspline.hpp:337:45: warning: reference 'v2_' cannot be declared 'mutable' [-fpermissive]
make[2]: *** [BermudanSwaption.o] Error 1

After compiling with -fpermissive I could get it compiled but the  warnings are still there whenever the compiler encounters
the mutable variables.

Thanks for Quantlib


----------------------------------------------------------------------

Comment By: Fahad Khan (fak98)
Date: 2011-06-21 18:07

Message:
I don't get any such issues on Fedora 15. Both on QuantLib-1.1 and trunk

$ gcc --version
gcc (GCC) 4.6.0 20110509 (Red Hat 4.6.0-7)


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