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This utility allows for the manual placement of objects without the need to have a global placement new operation nor the need for type-specific new operators. Issue #989
85 lines
2.7 KiB
C++
85 lines
2.7 KiB
C++
/*
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* \brief Utility for the manual placement of objects
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* \author Norman Feske
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* \date 2014-02-07
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*/
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/*
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* Copyright (C) 2014 Genode Labs GmbH
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*
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* This file is part of the Genode OS framework, which is distributed
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* under the terms of the GNU General Public License version 2.
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*/
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#ifndef _INCLUDE__UTIL__CONSTRUCT_AT_H_
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#define _INCLUDE__UTIL__CONSTRUCT_AT_H_
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#include <base/stdint.h>
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#include <base/printf.h>
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namespace Genode {
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template <typename T, typename... ARGS>
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static inline T *construct_at(void *, ARGS &&...);
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}
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/**
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* Construct object of given type at a specific location
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*
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* \param T object type
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* \param at desired object location
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* \param args list of arguments for the object constructor
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*
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* \return typed object pointer
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*
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* We use move semantics (ARGS &&) because otherwise the compiler would create
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* a temporary copy of all arguments that have a reference type and use a
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* reference to this copy instead of the original within this function.
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*
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* There is a slight difference between the object that is constructed by this
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* function and a common object of the given type. If the destructor of the
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* given type or of any base of the given type is virtual, the vtable of the
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* returned object references an empty delete(void *) operator for that
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* destructor. However, this shouldn't be a problem as an object constructed by
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* this function should never get destructed implicitely or through a delete
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* expression.
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*/
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template <typename T, typename... ARGS>
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static inline T * Genode::construct_at(void *at, ARGS &&... args)
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{
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/**
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* Utility to equip an existing type 'T' with a placement new operator
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*/
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struct Placeable : T
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{
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Placeable(ARGS &&... args) : T(args...) { }
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void * operator new (size_t, void *ptr) { return ptr; }
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void operator delete (void *, void *) { }
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/**
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* Standard delete operator
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*
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* As we explicitely define one version of the delete operator, the
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* compiler won't implicitely define any delete version for this class.
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* But if type T has a virtual destructor, the compiler implicitely
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* defines a 'virtual ~Placeable()' which needs the following operator.
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*/
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void operator delete (void *)
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{
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PERR("cxx: Placeable::operator delete (void *) not supported.");
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}
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};
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/*
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* If the args input to this function contains rvalues, the compiler would
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* use the according rvalue references as lvalues at the following call if
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* we don't cast them back to rvalue references explicitely. We can not use
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* lvalues here because the compiler can not bind them to rvalue references
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* as expected by Placeable.
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*/
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return new (at) Placeable(static_cast<ARGS &&>(args)...);
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}
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#endif /* _INCLUDE__UTIL__CONSTRUCT_AT_H_ */
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