Question

I am implementing a smart pointer class using generics and I wanted to force users of this class to properly construct the smart pointer using syntax such as

 MyReference<TestCls>(mytest3))

or

MyReference<TestCls> mytest4(new TestCls());

so I have used the explicit keyword on the CTOR, to prevent this:

MyReference aRef = NULL;

However due to unfortunate circumstances beyond my control, I am working on code that is compiled using the ancient MSVC++ 4.1 compiler. I get the following errors when I include the explicit keyword:

MyReference.h(49) : error C2501: ‘explicit’ : missing decl-specifiers
MyReference.h(51) : error C2143: syntax error : missing ‘;’ before ”
MyReference.h(52) : error C2238: unexpected token(s) preceding ‘:’
MyReference.h(52) : error C2059: syntax error : ‘int constant’

When I add a #define explicit those errors disappear.
This was a hack on my part, just to get the compiler to ignore the keyword. I’m guessing that this means that explicit is not supported by yon olde compiler.
Can someone confirm this and is there anyone out there with knowledge of a workaround solution for this?

Merci Beaucoups,
Dennis.

Answer 1

This site has a workaround for this, namely:

Unfortunately, older compilers may not
support the use of “explicit”, which
could be a headache. If you’re stuck
working with an out-of-date compiler
and can’t get one that has better
support for the C++ standard, your
best solution may be to take advantage
of the fact that only a single
implicit conversion will take place
for a given value. You can exploit
this by using an intermediate class
that implicitly creates an object of
each type, and then have your main
class implicitly create objects from
that class:

class proxy
{
    public:
    proxy(int x) : x(x) {} ;
    getValue() { return x; }

    private:
    int x;

};

class String
{
    // this will be equivalent of explicit
    String(proxy x) { /* create a string using x.getValue(); */ }
}