How to cast from list<T*> to list<const T*>

[Alexander Malkis]

//Consider:
class A { /*...*/ };

template<class T> class list {/*... */ };

void f(const list<const A*> lst) { /*...doesn't change the arg...*/ }

void g(list<A*> lst) {
f(lst); //Intuitively ok, but compiler rejects.
}

/* Compiler says:
error: conversion from `list<A*>' to non-scalar type `list<const A*>'
requested

Cast doesn't help either. What to do?
*/

 

[velthuijsen]

//Consider:
class A { /*...*/ };

template<class T> class list {/*... */ };

void f(const list<const A*> lst) { /*...doesn't change the arg...*/ }

void g(list<A*> lst) {
f(lst); //Intuitively ok, but compiler rejects.
}

/* Compiler says:
error: conversion from `list<A*>' to non-scalar type `list<const A*>'
requested

Cast doesn't help either. What to do?
*/

2 things

1) You are working on a list why not use the STL list(or one of the
other containers)?

2) did you really mean -> void f(const list<const A*> lst)
or did you want to do -> void f(const list<const A*>& lst)
?

That said because you are using a template there are two distinct
classes one is list<A*> and the other is list<const A*> which are in
no way related.
My first guess is that you'd need to write a conversion routine that
accepts a T and converts is to a const T.

My first guess seems to be supported by the compiler I'm using (VC++
7)
The intel compiler spits out the following error:
error: no suitable user-defined conversion from "list<A *>" to "const
list<const A *>" exists f(lst); //Intuitively ok, but compiler
rejects.

The M$ compiler spits out the following error:
error C2664: 'f' : cannot convert parameter 1 from 'list<T>' to 'const
list<T>' with [ T=A * ] and [ T=const A * ]

 

[Alexander Malkis]

1) You are working on a list why not use the STL list(or one of the
other containers)?

I have my own functions for lists which are not present in standard
libraries.

2) did you really mean -> void f(const list<const A*> lst)
or did you want to do -> void f(const list<const A*>& lst)
?

It's not essential for the matter of conversion.

My first guess is that you'd need to write a conversion routine that
accepts a T and converts is to a const T.

You mean maybe (T*) to (const T*) ?