Type validation helpers

The type validation helpers prevent accidental type conversions that would normally be permitted by the language.

The helpers permit a restricted set of types for the parameter, suppressing many categories of error-prone implicit conversions.

These helpers are useful primarily in macros, since macros cannot specify types for their parameters. For example, these helpers are employed extensively in the Error handling helpers to validate the types given to macro parameters.

Usage

The type validation helpers are defined in wil/common.h.

#include <wil/common.h>

verify_bool

template<typename T> constexpr bool verify_bool(const T& val);

Returns val converted to a bool. The val may be one of the following:

• bool
• BOOL
• BOOLEAN
• boolean (C++/CX)
• A class with an explicit bool conversion operator.

Other types are rejected and will generate a compile-time error of the form

Wrong Type: bool/BOOL/BOOLEAN/boolean expected

Examples

#define BEEP_IF(condition) do { if (wil::verify_bool(condition)) { Beep(); } } while ((void)0, 0)

wil::com_ptr<IUnknown> thing;
std::vector<int> vector;

BEEP_IF(thing);            // okay, com_ptr has bool conversion operator
BEEP_IF(InSendMessage());  // okay: InSendMessage returns BOOL
BEEP_IF(vector.empty());   // okay: std::vector<T>::empty() returns bool
BEEP_IF(CoRevertToSelf()); // not okay: CoRevertToSelf returns HRESULT, not bool

verify_BOOL

template<typename T> constexpr BOOL verify_BOOL(const T& val);

Returns val if it is of type BOOL. All other types are rejected with a compile-time error of the form

Wrong Type: BOOL expected

Examples

#define BEEP_IF(condition) do { if (wil::verify_BOOL(condition)) { Beep(); } } while ((void)0, 0)

wil::com_ptr<IUnknown> thing;
std::vector<int> vector;

BEEP_IF(thing);            // not okay: com_ptr is not a BOOL
BEEP_IF(InSendMessage());  // okay: InSendMessage returns BOOL
BEEP_IF(vector.empty());   // not okay: std::vector<T>::empty() returns bool
BEEP_IF(CoRevertToSelf()); // not okay: CoRevertToSelf returns HRESULT, not bool

verify_hresult

template<typename T> constexpr HRESULT verify_hresult(const T& val);

Returns val if it is of type HRESULT. All other types are rejected with a compile-time error of the form

Wrong Type: HRESULT expected

Examples

#define BEEP_IF_FAILED(hr) do { if (FAILED(wil::verify_hresult(hr))) { Beep(); } } while ((void)0, 0)

BEEP_IF_FAILED(InSendMessage());  // not okay: InSendMessage returns BOOL
BEEP_IF_FAILED(CoRevertToSelf()); // okay: CoRevertToSelf returns HRESULT