Assignment operator overloading for templated matrix class

Question

I am implementing assignment operator function for a template matrix class. It should take care of different datatype matrix assignments. eg Integer matrix is assigned to a double matrix. for that i have following declaration:

template<class U> MyMatrix<T>& operator= (const MyMatrix<U> &rhs) {...}

My problem is, if i implement the fuction within class declaration, it works. But if i implement it outside the class declaration like,

template<class T, class U> MyMatrix<T>& MyMatrix<T>::operator= (const MyMatrix<U> &rhs){...}

i get following error:

error: no declaration matches ‘MyMatrix<T>& MyMatrix<T>::operator=(const MyMatrix<U>&)’

What am i doing wrong?

An out-of-class definition would have to look like template<class T> template<class U> MyMatrix<T>& //etc. - you have a template within a template, not a template that takes 2 template parameters — UnholySheep
– UnholySheep, Commented Jun 6, 2023 at 10:07
@UnholySheep, can you please suggest resources where i can learn more about templates? Thanks — Renu
– Renu, Commented Jun 6, 2023 at 10:59
The only resource I can think of off the top of my head would be "Modern C++ Design" by Andrei Alexandrescu - but that is already a quite advanced text on templates. Otherwise I have mainly learnt by reading and working with code written by more experienced programmers — UnholySheep
– UnholySheep, Commented Jun 6, 2023 at 11:41

user21908670 · Accepted Answer · 2023-06-06 12:46:24Z

1

When providing out of class definition of a member template you've to provide the template parameter clause correspondimg to both the class template as well as the member template as shown below:

template<class T> // parameter clause for class template 
template<class U> // parameter clause for member template
MyMatrix<T>& MyMatrix<T>::operator= (const MyMatrix<U> &rhs)
{  // code here
}

answered Jun 6, 2023 at 12:46

user21908670

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