為ScopedGuard禁用“未使用的變量”

Question

林與安德烈Alexandrescu的和彼得魯杜米特Marginean玩范圍的警衛對象

使用-Wall -Werror進行編譯時，會出現“未使用的變量”錯誤。 以下代碼取自LOKI

    class ScopeGuardImplBase
{
    ScopeGuardImplBase& operator =(const ScopeGuardImplBase&);

protected:

    ~ScopeGuardImplBase()
    {}

    ScopeGuardImplBase(const ScopeGuardImplBase& other) throw() 
        : dismissed_(other.dismissed_)
    {
        other.Dismiss();
    }

    template <typename J>
    static void SafeExecute(J& j) throw() 
    {
        if (!j.dismissed_)
            try
            {
                j.Execute();
            }
            catch(...)
            {}
    }

    mutable bool dismissed_;

public:
    ScopeGuardImplBase() throw() : dismissed_(false) 
    {}

    void Dismiss() const throw() 
    {
        dismissed_ = true;
    }
};

////////////////////////////////////////////////////////////////
///
/// \typedef typedef const ScopeGuardImplBase& ScopeGuard
/// \ingroup ExceptionGroup
///
/// See Andrei's and Petru Marginean's CUJ article
/// http://www.cuj.com/documents/s=8000/cujcexp1812alexandr/alexandr.htm
///
/// Changes to the original code by Joshua Lehrer:
/// http://www.lehrerfamily.com/scopeguard.html
////////////////////////////////////////////////////////////////

typedef const ScopeGuardImplBase& ScopeGuard;

template <typename F>
class ScopeGuardImpl0 : public ScopeGuardImplBase
{
public:
    static ScopeGuardImpl0<F> MakeGuard(F fun)
    {
        return ScopeGuardImpl0<F>(fun);
    }

    ~ScopeGuardImpl0() throw() 
    {
        SafeExecute(*this);
    }

    void Execute() 
    {
        fun_();
    }

protected:
    ScopeGuardImpl0(F fun) : fun_(fun) 
    {}

    F fun_;
};

template <typename F> 
inline ScopeGuardImpl0<F> MakeGuard(F fun)
{
    return ScopeGuardImpl0<F>::MakeGuard(fun);
}

問題在於用法：

ScopeGuard scope_guard = MakeGuard(&foo);

這只是

const ScopeGuardImplBase& scope_guard = ScopeGuardImpl0<void(*)()>(&foo);

我正在使用Macro在應對結束時采取一些措施：

#define SCOPE_GUARD ScopedGuard scope_guard = MakeGuard

這樣，用戶可以打電話

SCOPE_GUARD(&foo, param) ...

此宏很難禁用未使用的警告。

有人可以幫助我更好地理解這一點，也許可以在不使用-Wno-unused-variable的情況下提供解決方案嗎？

Answer 1

您可以嘗試使用舊方法：

 (void)scope_guard;