Non-Local Operator Assignment Is Not Guaranteed To Be Atomic Number

Initializes an object from another object

[edit]Syntax

Tobjectother (1)
Tobjectother (2) (until C++11)
fother (3)
other (4)
object

Tobject

(5)
TarrayNother (6)

[edit]Explanation

Copy initialization is performed in the following situations:

1) when a named variable (automatic, static, or thread-local) of a non-reference type is declared with the initializer consisting of an equals sign followed by an expression.

2)(until C++11)when a named variable of a scalar type is declared with the initializer consisting of an equals sign followed by a brace-enclosed expression (Note: as of C++11, this is classified as list initialization, and narrowing conversion is not allowed).

3) when passing an argument to a function by value

4) when returning from a function that returns by value

5) when throwing or catching an exception by value

6) as part of aggregate initialization, to initialize each element for which an initializer is provided

The effects of copy initialization are:

  • First, if is a class type and the initializer is a prvalue expression whose cv-unqualified type is the same class as , the initializer expression itself, rather than a temporary materialized from it, is used to initialize the destination object: see copy elision
(since C++17)
  • If is a class type and the cv-unqualified version of the type of other is or a class derived from , the non-explicit constructors of are examined and the best match is selected by overload resolution. The constructor is then called to initialize the object.
  • If is a class type, and the cv-unqualified version of the type of other is not or derived from , or if is non-class type, but the type of other is a class type, user-defined conversion sequences that can convert from the type of other to (or to a type derived from T if T is a class type and a conversion function is available) are examined and the best one is selected through overload resolution. The result of the conversion, which is a prvalue temporary(until C++17)prvalue expression(since C++17) if a converting constructor was used, is then used to direct-initialize the object. The last step is usually optimized out and the result of the conversion is constructed directly in the memory allocated for the target object, but the appropriate constructor (move or copy) is required to be accessible even though it's not used.(until C++17)
  • Otherwise (if neither nor the type of other are class types), standard conversions are used, if necessary, to convert the value of other to the cv-unqualified version of .

[edit]Notes

Copy-initialization is less permissive than direct-initialization: explicit constructors are not converting constructors and are not considered for copy-initialization.

In addition, the implicit conversion in copy-initialization must produce directly from the initializer, while, e.g. direct-initialization expects an implicit conversion from the initializer to an argument of 's constructor.

If other is an rvalue expression, move constructor will be selected by overload resolution and called during copy-initialization. There is no such term as move-initialization.

Implicit conversion is defined in terms of copy-initialization: if an object of type can be copy-initialized with expression , then is implicitly convertible to .

The equals sign, , in copy-initialization of a named variable is not related to the assignment operator. Assignment operator overloads have no effect on copy-initialization.

[edit]Example

Run this code

#include <string>#include <utility>#include <memory>   struct A { operator int(){return12;}};   struct B { B(int){}};   int main(){std::string s ="test";// OK: constructor is non-explicitstd::string s2 = std::move(s);// this copy-initialization performs a move   // std::unique_ptr<int> p = new int(1); // error: constructor is explicitstd::unique_ptr<int> p(new int(1));// OK: direct-initialization     int n =3.14;// floating-integral conversionconstint b = n;// const doesn't matterint c = b;// ...either way     A a; B b0 =12;// B b1 = a; //< error: conversion from 'A' to non-scalar type 'B' requested B b2{a};// < identical, calling A::operator int(), then B::B(int) B b3 ={a};// <auto b4 = B{a};// <   // b0 = a; //< error, assignment operator overload needed }

[edit]See also

struct Exp {explicit Exp(constchar*){}};// not convertible from const char* Exp e1("abc");// OK Exp e2 ="abc";// Error, copy-initialization does not consider explicit constructor   struct Imp { Imp(constchar*){}};// convertible from const char* Imp i1("abc");// OK Imp i2 ="abc";// OK
struct S { S(std::string){}};// implicitly convertible from std::string S s("abc");// OK: conversion from const char[4] to std::string S s ="abc";// Error: no conversion from const char[4] to S S s ="abc"s;// OK: conversion from std::string to S

IUPAC announces the verification of the discoveries of four new chemical elements: The 7th period of the periodic table of elements is complete.


The fourth IUPAC/IUPAP Joint Working Party (JWP) on the priority of claims to the discovery of new elements has reviewed the relevant literature for elements 113, 115, 117, and 118 and has determined that the claims for discovery of these elements have been fulfilled, in accordance with the criteria for the discovery of elements of the IUPAP/IUPAC Transfermium Working Group (TWG) 1991 discovery criteria. These elements complete the 7th row of the periodic table of the elements, and the discoverers from Japan, Russia and the USA will now be invited to suggest permanent names and symbols. The new elements and assigned priorities of discovery are as follows:

Element 113 (temporary working name and symbol: ununtrium, Uut)
The RIKEN collaboration team in Japan have fulfilled the criteria for element Z=113 and will be invited to propose a permanent name and symbol.

Elements 115, 117, and 118 (temporary working names and symbols: ununpentium, Uup; ununseptium, Uus; and ununoctium, Uuo)
The collaboration between the Joint Institute for Nuclear Research in Dubna, Russia; Lawrence Livermore National Laboratory, California, USA; and Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA have fulfilled the criteria for element Z=115, 117 and will be invited to propose permanent names and symbols.

The collaboration between the Joint Institute for Nuclear Research in Dubna, Russia and Lawrence Livermore National Laboratory, California, USA have fulfilled the criteria for element Z=118 and will be invited to propose a permanent name and symbol.

The priorities for four new chemical elements are being introduced simultaneously, after the careful verification of the discoveries and priorities. The decisions are detailed in two reports by the Joint Working Party (JWP), which includes experts drawn from IUPAC and IUPAP (the International Union of Pure and Applied Physics). These reports will be published in an early 2016 issue of the IUPAC journal Pure and Applied Chemistry (PAC).The JWP has reviewed the relevant literature pertaining to several claims of these new elements. The JWP has determined that the RIKEN collaboration have fulfilled the criteria for the discovery of element with atomic numbers Z=113. Several studies published from 2004 to 2012 have been construed as sufficient to ratify the discovery and priority.

In the same PAC report, the JWP also concluded that the collaborative work between scientists from the Joint Institute for Nuclear Research in Dubna, Russia; from Lawrence Livermore National Laboratory, California, USA; and from Oak Ridge National Laboratory, Oak Ridge, Tennessee, USA (the Dubna-Livermore-Oak Ridge collaborations), starting in 2010, and subsequently confirmed in 2012 and 2013, have met the criteria for discovery of the elements with atomic numbers Z=115 and Z=117.

Finally, in a separate PAC article the Dubna-Livermore collaboration started in 2006 is reported as having satisfied the criteria for discovery of element Z=118.

“A particular difficulty in establishing these new elements is that they decay into hitherto unknown isotopes of slightly lighter elements that also need to be unequivocally identified” commented JWP chair Professor Paul J. Karol, “but in the future we hope to improve methods that can directly measure the atomic number, Z“.

“The chemistry community is eager to see its most cherished table finally being completed down to the seventh row. IUPAC has now initiated the process of formalizing names and symbols for these elements temporarily named as ununtrium, (Uut or element 113), ununpentium (Uup, element 115), ununseptium (Uus, element 117), and ununoctium  (Uuo, element 118)” said Professor Jan Reedijk, President of the Inorganic Chemistry Division of IUPAC.

The proposed names and symbols will be checked by the Inorganic Chemistry Division of IUPAC for consistency, translatability into other languages, possible prior historic use for other cases, etc. New elements can be named after a mythological concept, a mineral, a place or country, a property or a scientist (see: W.H. Koppenol, PAC 74 (2002) 787-791). After Divisional acceptance, the names and two-letter symbols will be presented for public review for five months, before the highest body of IUPAC, the Council, will make a final decision on the names of these new chemical elements and their two-letter symbols and their introduction into the Periodic Table of the Elements.

“As the global organization that provides objective scientific expertise and develops the essential tools for the application and communication of chemical knowledge for the benefit of humankind, the International Union of Pure and Applied Chemistry is pleased and honored to make this announcement concerning elements 113, 115, 117, and 118 and the completion of the seventh row of the periodic table of the elements,” said IUPAC President Dr. Mark C. Cesa, adding that, “we are excited about these new elements, and we thank the dedicated scientists who discovered them for their painstaking work, as well the members of the IUPAC/IUPAP Joint Working Party for completing their essential and critically important task.”

For further information, contact Dr. Lynn M. Soby, Executive Director, IUPAC, at secretariat@iupac.org or lsoby@iupac.org.

> Download IUPAC-Press-Release_30Dec2015


PS: Published online 21 January 2016, in Pure and Applied Chemistry: P.J. Karol, R.C. Barber, B.M. Sherrill, E. Vardaci, T. Yamazaki, Pure Appl. Chem. 88 (2016) 139; http://dx.doi.org/10.1515/pac-2015-0502 and ibid., Pure Appl. Chem. 88 (2016) 155; http://dx.doi.org/10.1515/pac-2015-0501

PS2: Announced on 8 June 2016: IUPAC is naming the four new elements nihonium, moscovium, tennessine, and oganesson

Tags: element 113, element 115, element 117, element 118, IUPAC/IUPAP Joint Working Party, chemical elements, periodic table

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