mirror of https://github.com/bsnes-emu/bsnes.git
92 lines
3.0 KiB
C++
Executable File
92 lines
3.0 KiB
C++
Executable File
#ifndef NALL_PROPERTY_HPP
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#define NALL_PROPERTY_HPP
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//nall::property implements ownership semantics into container classes
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//example: property<owner>::readonly<type> implies that only owner has full
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//access to type; and all other code has readonly access.
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//
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//this code relies on extended friend semantics from C++0x to work, as it
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//declares a friend class via a template paramter. it also exploits a bug in
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//G++ 4.x to work even in C++98 mode.
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//
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//if compiling elsewhere, simply remove the friend class and private semantics
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//property can be used either of two ways:
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//struct foo {
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// property<foo>::readonly<bool> x;
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// property<foo>::readwrite<int> y;
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//};
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//-or-
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//struct foo : property<foo> {
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// readonly<bool> x;
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// readwrite<int> y;
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//};
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//return types are const T& (byref) instead of T (byval) to avoid major speed
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//penalties for objects with expensive copy constructors
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//operator-> provides access to underlying object type:
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//readonly<Object> foo;
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//foo->bar();
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//... will call Object::bar();
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//operator='s reference is constant so as to avoid leaking a reference handle
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//that could bypass access restrictions
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//both constant and non-constant operators are provided, though it may be
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//necessary to cast first, for instance:
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//struct foo : property<foo> { readonly<int> bar; } object;
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//int main() { int value = const_cast<const foo&>(object); }
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//writeonly is useful for objects that have non-const reads, but const writes.
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//however, to avoid leaking handles, the interface is very restricted. the only
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//way to write is via operator=, which requires conversion via eg copy
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//constructor. example:
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//struct foo {
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// foo(bool value) { ... }
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//};
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//writeonly<foo> bar;
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//bar = true;
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namespace nall {
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template<typename C> struct property {
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template<typename T> struct traits { typedef T type; };
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template<typename T> struct readonly {
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const T* operator->() const { return &value; }
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const T& operator()() const { return value; }
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operator const T&() const { return value; }
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private:
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T* operator->() { return &value; }
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operator T&() { return value; }
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const T& operator=(const T& value_) { return value = value_; }
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T value;
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friend class traits<C>::type;
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};
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template<typename T> struct writeonly {
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void operator=(const T& value_) { value = value_; }
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private:
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const T* operator->() const { return &value; }
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const T& operator()() const { return value; }
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operator const T&() const { return value; }
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T* operator->() { return &value; }
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operator T&() { return value; }
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T value;
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friend class traits<C>::type;
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};
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template<typename T> struct readwrite {
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const T* operator->() const { return &value; }
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const T& operator()() const { return value; }
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operator const T&() const { return value; }
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T* operator->() { return &value; }
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operator T&() { return value; }
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const T& operator=(const T& value_) { return value = value_; }
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T value;
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};
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};
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}
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#endif
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