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

Right value reference and left value

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• ​ ​ The role of R-value reference ​​
• ​ ​ The concepts of left and right values ​​
• ​ ​ The difference between right and left references ​​
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The role of R-value reference

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

The purpose has two aspects ：

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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

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2. Left values can address , And right value can't .
3. Left values can be assigned , Right values cannot be assigned , It can be used to assign values to left values .
4. 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 ）.
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