Re: Verify and expression

Frederick Gotham <>
14 Oct 2006 16:56:21 -0400
Andrei Alexandrescu (See Website For Email) posted:

  bool ok = verify( start_bus() );

I prefer this:

    bool ok = start_bus();


, as it separates the "actual" code from the "debugging" code.

That introduces a gratuitous variable. if (!start_bus()) assert(false);
would avoid that.

The original code contained such a variable, so I took the liberty of
presuming it had a purpose. There's not much merit in writing "assert
(false)", as your error message will simply describe the error as "false"
rather than "start_bus()".

Essentially, I think the OP wants a function/macro that works exactly like
assert, except that it still evaluates its argument when in Release Mode.
Furthermore, I think the OP wants to retain the value of the expression. The
following might be a start:

#include <iostream>
#include <ostream>
#include <cstdlib>

template<class T>
T const &Verify(T const &expr,char const *const str)
        std::cerr << "VERIFY Failure. \"" __FILE__ "\": Line "
                  << __LINE__ << " -- " << str << std::endl;


    return expr;

template<class T>
T &Verify(T &expr,char const *const str)
    return const_cast<T&>(
        Verify(const_cast<T const&>(expr),str)

#define VERIFY(expr) (Verify((expr),#expr))

class MyClass {

    MyClass() {}

    operator double() const { return 56.8; }

    operator bool() const { return false; }


int main()
    MyClass obj;

    double val = VERIFY(obj);

    MyClass &r = VERIFY(obj);

    std::cout << val << std::endl;


Frederick Gotham

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