tmp/tmpkrlrq6jc/{from.md → to.md}
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### Pointer optimization barrier <a id="ptr.launder">[[ptr.launder]]</a>
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``` cpp
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template <class T> constexpr T* launder(T* p) noexcept;
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```
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*Requires:* `p` represents the address *A* of a byte in memory. An
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object *X* that is within its lifetime ([[basic.life]]) and whose type
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is similar ([[conv.qual]]) to `T` is located at the address *A*. All
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bytes of storage that would be reachable through the result are
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reachable through `p` (see below).
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*Returns:* A value of type `T *` that points to `X`.
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*Remarks:* An invocation of this function may be used in a core constant
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expression whenever the value of its argument may be used in a core
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constant expression. A byte of storage is reachable through a pointer
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value that points to an object *Y* if it is within the storage occupied
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by *Y*, an object that is pointer-interconvertible with *Y*, or the
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immediately-enclosing array object if *Y* is an array element. The
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program is ill-formed if `T` is a function type or cv `void`.
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[*Note 1*: If a new object is created in storage occupied by an
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existing object of the same type, a pointer to the original object can
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be used to refer to the new object unless the type contains `const` or
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reference members; in the latter cases, this function can be used to
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obtain a usable pointer to the new object.
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See [[basic.life]]. — *end note*]
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[*Example 1*:
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``` cpp
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struct X { const int n; };
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X *p = new X{3};
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const int a = p->n;
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new (p) X{5}; // p does not point to new object ([basic.life]) because X::n is const
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const int b = p->n; // undefined behavior
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const int c = std::launder(p)->n; // OK
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```
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— *end example*]
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