rspec/rules/S5415/cfamily/rule.adoc

Calling ``++std::move++`` on objects that cannot be moved is suspicious and might hide nasty performance bug.


This can happen when calling ``++std::move++`` with const argument or with non-movable types.


This can also happen when passing the result of ``++std::move++`` as a const reference argument.  In this case, no object will be moved since the result is in a context where calling the move constructor is not possible. It makes sense to call ``++std::move++`` on a function argument when:

* The result of ``++std::move++`` is passed as an r-value reference.
* The result of ``++std::move++`` is passed by copy.


== Noncompliant Code Example

----
struct NonMovable{
  NonMovable() = default;
  NonMovable(NonMovable&) = default;
};

void f(NonMovable s);
void f(std::string s);
void g(const std::string &s);

void test() {
  std::string s="****";
  f(std::move(s));
  g(std::move(s)); // Noncompliant: s is cast back to const l-value reference. s will not be moved.

  const std::string constS="***";
  f(std::move(constS)); // Noncompliant: constS will not be moved.

  NonMovable t;
  f(std::move(t)); // Noncompliant: std::move is useless on non-movable objects like t. Copy constructor is called.
}
----


== Compliant Solution

----
struct Movable{
  Movable() = default;
  Movable(Movable&) = default;
  Movable(Movable&&) = default;
};

void f(Movable);
void f(std::string s);
void g(const std::string &s);

void test() {
  std::string s="****";
  f(std::move(s)); // Compliant:  move constructor is called.
  g(s); // Compliant: no misleading std::move is used.

  Movables t;
  f(std::move(t)); // Compliant: move constructor is called.
}
----


== See

* https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines#es56-write-stdmove-only-when-you-need-to-explicitly-move-an-object-to-another-scope[{cpp} Core Guidelines ES.56] - Write "std::move()" only when you need to explicitly move an object to another scope


ifdef::rspecator-view[]
== Comments And Links
(visible only on this page)

include::comments-and-links.adoc[]
endif::rspecator-view[]