CODEWITHSUNDEEP
c++visual-studio-2010lambda
Grzenio
Grzenio

Reputation: 36639

Lambda expressions in VS 2010 as opposed to gcc

I am trying to compile my code in VS 2010 that compiles and works in gcc, but I get a weird error on a lambda expression:

   std::function<double (size_t level, size_t q)> doLevel = [&](size_t level, size_t q)
   {  //line 52
       double thisLevelP = density(q, data[level]);
       if(level==T-1) return thisLevelP;
       if(level==t-1) return  thisLevelP*A(q,state)*doLevel(level+1,state);
       double continuation = 0.0;
       for(size_t i=0; i<Q; ++i)
       {
           continuation += A(q, i)*doLevel(level+1, i);
       }
       return thisLevelP*continuation;
   };

The error is:

Error   1   error C2086: 'size_t &_T' : redefinition    c:\users\ga1009\documents\phd\cpp\pmi\cpp\test\baumiterationtest.cpp    52
Error   2   error C2661: '`anonymous-namespace'::`anonymous-namespace'::<lambda1>::<lambda1>' : no overloaded function takes 8 arguments    c:\users\ga1009\documents\phd\cpp\pmi\cpp\test\baumiterationtest.cpp    52

What is wrong?

Upvotes: 0

Views: 328

Answers (1)

odinthenerd
odinthenerd

Reputation: 5552

As seen in the comments above by chris, lambdas with multiple return statements need an explicit return type which can be declared like this ->double.

More importantly though the offending line is the variable named t which is captured by the lambda. I originally though this was a name clash but as STL correctly points out it happens with any two names which are the same except one is capital. This is a compiler bug which is known and has been fixed in the newest versions. 

double density(std::size_t, int)
{
    return 0;
}
double A(std::size_t, int)
{
    return 0;
}
int main(int argc, char *argv[])
{
    int data[] = {1,2,3};
    std::size_t T = 1;
    std::size_t t = 2;   //<<<<< change this name and it compiles
    std::size_t state = 3;
    std::size_t Q = 4;
    std::function<double (int,int)> doLevel = [&](int level, int q)->double
   { 
       double thisLevelP = density(q, data[level]);
      if(level==T-1) 
           return thisLevelP;
      if(level==t-1) 
           return  thisLevelP*A(q,state)*doLevel(level+1,state);
       double continuation = 0.0;
       for(size_t i=0; i<Q; ++i)
       {
           continuation += A(q, i)*doLevel(level+1, i);
       }
       return thisLevelP*continuation;
   };
}

Upvotes: 4

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