What is an R-value reference and what is the difference between it and an l-value?

Right value reference and left value reference

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• ​ ​ Right quoting ​​
• ​ ​ The concepts of left and right values ：​​
• ​ ​ The difference between right and left references ：​​
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Right quoting

The right quotation is C++11 New features introduced in , It implements transfer semantics and precise delivery . Its main

The purpose has two aspects ：

1. 1. 
      
2. Eliminate unnecessary copy of objects when two objects interact , Save computing and storage resources , Increase of efficiency .
3. Can be more concise and clear definition of generic functions .
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The concepts of left and right values ：

The left value ： Can take address for expression 、 Or named objects / Variable . A persistent object that still exists after the end of an expression .

Right value ： Cannot address an expression , Or anonymous objects . A temporary object that no longer exists at the end of an expression .

The difference between right and left references ：

3. 3. 
      
4. Left values can address , And right value can't .
5. Left values can be assigned , Right values cannot be assigned , It can be used to assign values to left values .
6. Left variable , The right value is immutable （ For foundation types only , The right value reference of user-defined type can be through member function
   change ）.
   3.