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Co-authored-by: Herb Sutter <herb.sutter@gmail.com>
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@ -4820,7 +4820,7 @@ Constructor rules:
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* [C.44: Prefer default constructors to be simple and non-throwing](#Rc-default00)
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* [C.44: Prefer default constructors to be simple and non-throwing](#Rc-default00)
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* [C.45: Don't define a default constructor that only initializes data members; use member initializers instead](#Rc-default)
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* [C.45: Don't define a default constructor that only initializes data members; use member initializers instead](#Rc-default)
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* [C.46: By default, declare single-argument constructors `explicit`](#Rc-explicit)
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* [C.46: By default, declare single-argument constructors `explicit`](#Rc-explicit)
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* [C.47: Define and initialize member variables in the order of member declaration](#Rc-order)
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* [C.47: Define and initialize data members in the order of member declaration](#Rc-order)
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* [C.48: Prefer default member initializers to member initializers in constructors for constant initializers](#Rc-in-class-initializer)
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* [C.48: Prefer default member initializers to member initializers in constructors for constant initializers](#Rc-in-class-initializer)
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* [C.49: Prefer initialization to assignment in constructors](#Rc-initialize)
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* [C.49: Prefer initialization to assignment in constructors](#Rc-initialize)
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* [C.50: Use a factory function if you need "virtual behavior" during initialization](#Rc-factory)
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* [C.50: Use a factory function if you need "virtual behavior" during initialization](#Rc-factory)
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@ -5018,10 +5018,10 @@ These operations disagree about copy semantics. This will lead to confusion and
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##### Enforcement
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##### Enforcement
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* (Complex) A copy/move constructor and the corresponding copy/move assignment operator should write to the same member variables at the same level of dereference.
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* (Complex) A copy/move constructor and the corresponding copy/move assignment operator should write to the same data members at the same level of dereference.
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* (Complex) Any member variables written in a copy/move constructor should also be initialized by all other constructors.
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* (Complex) Any data members written in a copy/move constructor should also be initialized by all other constructors.
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* (Complex) If a copy/move constructor performs a deep copy of a member variable, then the destructor should modify the member variable.
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* (Complex) If a copy/move constructor performs a deep copy of a data member, then the destructor should modify the data member.
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* (Complex) If a destructor is modifying a member variable, that member variable should be written in any copy/move constructors or assignment operators.
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* (Complex) If a destructor is modifying a data member, that data member should be written in any copy/move constructors or assignment operators.
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## <a name="SS-dtor"></a>C.dtor: Destructors
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## <a name="SS-dtor"></a>C.dtor: Destructors
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@ -5144,9 +5144,9 @@ Here `p` refers to `pp` but does not own it.
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##### Enforcement
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##### Enforcement
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* (Simple) If a class has pointer or reference member variables that are owners
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* (Simple) If a class has pointer or reference members that are owners
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(e.g., deemed owners by using `gsl::owner`), then they should be referenced in its destructor.
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(e.g., deemed owners by using `gsl::owner`), then they should be referenced in its destructor.
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* (Hard) Determine if pointer or reference member variables are owners when there is no explicit statement of ownership
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* (Hard) Determine if pointer or reference members are owners when there is no explicit statement of ownership
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(e.g., look into the constructors).
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(e.g., look into the constructors).
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### <a name="Rc-dtor-ptr"></a>C.32: If a class has a raw pointer (`T*`) or reference (`T&`), consider whether it might be owning
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### <a name="Rc-dtor-ptr"></a>C.32: If a class has a raw pointer (`T*`) or reference (`T&`), consider whether it might be owning
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@ -5491,7 +5491,7 @@ If a valid object cannot conveniently be constructed by a constructor, [use a fa
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##### Enforcement
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##### Enforcement
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* (Simple) Every constructor should initialize every member variable (either explicitly, via a delegating ctor call or via default construction).
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* (Simple) Every constructor should initialize every data member (either explicitly, via a delegating ctor call or via default construction).
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* (Unknown) If a constructor has an `Ensures` contract, try to see if it holds as a postcondition.
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* (Unknown) If a constructor has an `Ensures` contract, try to see if it holds as a postcondition.
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##### Note
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##### Note
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@ -5784,7 +5784,7 @@ Using default member initializers lets the compiler generate the function for yo
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##### Enforcement
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##### Enforcement
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(Simple) A default constructor should do more than just initialize member variables with constants.
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(Simple) A default constructor should do more than just initialize data members with constants.
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### <a name="Rc-explicit"></a>C.46: By default, declare single-argument constructors explicit
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### <a name="Rc-explicit"></a>C.46: By default, declare single-argument constructors explicit
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@ -5824,7 +5824,7 @@ Copy and move constructors should not be made `explicit` because they do not per
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(Simple) Single-argument constructors should be declared `explicit`. Good single argument non-`explicit` constructors are rare in most code bases. Warn for all that are not on a "positive list".
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(Simple) Single-argument constructors should be declared `explicit`. Good single argument non-`explicit` constructors are rare in most code bases. Warn for all that are not on a "positive list".
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### <a name="Rc-order"></a>C.47: Define and initialize member variables in the order of member declaration
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### <a name="Rc-order"></a>C.47: Define and initialize data members in the order of member declaration
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##### Reason
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##### Reason
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@ -5894,7 +5894,7 @@ How would a maintainer know whether `j` was deliberately uninitialized (probably
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##### Enforcement
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##### Enforcement
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* (Simple) Every constructor should initialize every member variable (either explicitly, via a delegating ctor call or via default construction).
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* (Simple) Every constructor should initialize every data member (either explicitly, via a delegating ctor call or via default construction).
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* (Simple) Default arguments to constructors suggest a default member initializer might be more appropriate.
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* (Simple) Default arguments to constructors suggest a default member initializer might be more appropriate.
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### <a name="Rc-initialize"></a>C.49: Prefer initialization to assignment in constructors
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### <a name="Rc-initialize"></a>C.49: Prefer initialization to assignment in constructors
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@ -7719,7 +7719,7 @@ Consider making such a class a `struct` -- that is, a behaviorless bunch of vari
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int y {0};
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int y {0};
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};
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};
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Note that we can put default initializers on member variables: [C.49: Prefer initialization to assignment in constructors](#Rc-initialize).
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Note that we can put default initializers on data members: [C.49: Prefer initialization to assignment in constructors](#Rc-initialize).
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##### Note
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##### Note
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@ -10918,7 +10918,7 @@ Many such errors are introduced during maintenance years after the initial imple
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##### Example
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##### Example
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This rule covers member variables.
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This rule covers data members.
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class X {
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class X {
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public:
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public:
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@ -14554,7 +14554,7 @@ but we can mention:
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and some older versions of [GCC](https://gcc.gnu.org/wiki/ThreadSafetyAnnotation)
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and some older versions of [GCC](https://gcc.gnu.org/wiki/ThreadSafetyAnnotation)
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have some support for static annotation of thread safety properties.
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have some support for static annotation of thread safety properties.
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Consistent use of this technique turns many classes of thread-safety errors into compile-time errors.
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Consistent use of this technique turns many classes of thread-safety errors into compile-time errors.
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The annotations are generally local (marking a particular member variable as guarded by a particular mutex),
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The annotations are generally local (marking a particular data member as guarded by a particular mutex),
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and are usually easy to learn. However, as with many static tools, it can often present false negatives;
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and are usually easy to learn. However, as with many static tools, it can often present false negatives;
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cases that should have been caught but were allowed.
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cases that should have been caught but were allowed.
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@ -15784,7 +15784,7 @@ Sometimes C++ code allocates the `volatile` memory and shares it with "elsewhere
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##### Example, bad
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##### Example, bad
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`volatile` local variables are nearly always wrong -- how can they be shared with other languages or hardware if they're ephemeral?
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`volatile` local variables are nearly always wrong -- how can they be shared with other languages or hardware if they're ephemeral?
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The same applies almost as strongly to member variables, for the same reason.
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The same applies almost as strongly to data members, for the same reason.
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void f()
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void f()
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{
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{
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@ -15793,7 +15793,7 @@ The same applies almost as strongly to member variables, for the same reason.
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}
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}
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class My_type {
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class My_type {
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volatile int i = 0; // suspicious, volatile member variable
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volatile int i = 0; // suspicious, volatile data member
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// etc.
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// etc.
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};
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};
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@ -15803,7 +15803,7 @@ In C++, unlike in some other languages, `volatile` has [nothing to do with synch
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##### Enforcement
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##### Enforcement
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* Flag `volatile T` local and member variables; almost certainly you intended to use `atomic<T>` instead.
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* Flag `volatile T` local and data members; almost certainly you intended to use `atomic<T>` instead.
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* ???
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* ???
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### <a name="Rconc-signal"></a>CP.201: ??? Signals
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### <a name="Rconc-signal"></a>CP.201: ??? Signals
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@ -16959,7 +16959,7 @@ it offers to its users.
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##### Enforcement
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##### Enforcement
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* Flag a member function that is not marked `const`, but that does not perform a non-`const` operation on any member variable.
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* Flag a member function that is not marked `const`, but that does not perform a non-`const` operation on any data member.
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### <a name="Rconst-ref"></a>Con.3: By default, pass pointers and references to `const`s
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### <a name="Rconst-ref"></a>Con.3: By default, pass pointers and references to `const`s
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@ -21181,7 +21181,7 @@ Type safety profile summary:
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Prefer [construction](#Res-construct) or [named casts](#Res-casts-named) or `T{expression}`.
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Prefer [construction](#Res-construct) or [named casts](#Res-casts-named) or `T{expression}`.
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* <a name="Pro-type-init"></a>Type.5: Don't use a variable before it has been initialized:
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* <a name="Pro-type-init"></a>Type.5: Don't use a variable before it has been initialized:
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[always initialize](#Res-always).
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[always initialize](#Res-always).
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* <a name="Pro-type-memberinit"></a>Type.6: Always initialize a member variable:
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* <a name="Pro-type-memberinit"></a>Type.6: Always initialize a data member:
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[always initialize](#Res-always),
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[always initialize](#Res-always),
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possibly using [default constructors](#Rc-default0) or
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possibly using [default constructors](#Rc-default0) or
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[default member initializers](#Rc-in-class-initializer).
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[default member initializers](#Rc-in-class-initializer).
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@ -22244,9 +22244,9 @@ Modernization can be much faster, simpler, and safer when supported with analysi
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This section contains follow-up material on rules and sets of rules.
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This section contains follow-up material on rules and sets of rules.
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In particular, here we present further rationale, longer examples, and discussions of alternatives.
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In particular, here we present further rationale, longer examples, and discussions of alternatives.
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### <a name="Sd-order"></a>Discussion: Define and initialize member variables in the order of member declaration
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### <a name="Sd-order"></a>Discussion: Define and initialize data members in the order of member declaration
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Member variables are always initialized in the order they are declared in the class definition, so write them in that order in the constructor initialization list. Writing them in a different order just makes the code confusing because it won't run in the order you see, and that can make it hard to see order-dependent bugs.
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Data members are always initialized in the order they are declared in the class definition, so write them in that order in the constructor initialization list. Writing them in a different order just makes the code confusing because it won't run in the order you see, and that can make it hard to see order-dependent bugs.
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class Employee {
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class Employee {
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string email, first, last;
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string email, first, last;
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In this example, `email` will be constructed before `first` and `last` because it is declared first. That means its constructor will attempt to use `first` and `last` too soon -- not just before they are set to the desired values, but before they are constructed at all.
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In this example, `email` will be constructed before `first` and `last` because it is declared first. That means its constructor will attempt to use `first` and `last` too soon -- not just before they are set to the desired values, but before they are constructed at all.
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If the class definition and the constructor body are in separate files, the long-distance influence that the order of member variable declarations has over the constructor's correctness will be even harder to spot.
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If the class definition and the constructor body are in separate files, the long-distance influence that the order of data member declarations has over the constructor's correctness will be even harder to spot.
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**References**:
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**References**:
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@ -22988,7 +22988,7 @@ Alternatively, we will decide that no change is needed and delete the entry.
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* Should there be inline namespaces (à la `std::literals::*_literals`)?
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* Should there be inline namespaces (à la `std::literals::*_literals`)?
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* Avoid implicit conversions
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* Avoid implicit conversions
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* Const member functions should be thread safe ... aka, but I don't really change the variable, just assign it a value the first time it's called ... argh
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* Const member functions should be thread safe ... aka, but I don't really change the variable, just assign it a value the first time it's called ... argh
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* Always initialize variables, use initialization lists for member variables.
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* Always initialize variables, use initialization lists for data members.
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* Anyone writing a public interface which takes or returns `void*` should have their toes set on fire. That one has been a personal favorite of mine for a number of years. :)
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* Anyone writing a public interface which takes or returns `void*` should have their toes set on fire. That one has been a personal favorite of mine for a number of years. :)
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* Use `const`-ness wherever possible: member functions, variables and (yippee) `const_iterators`
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* Use `const`-ness wherever possible: member functions, variables and (yippee) `const_iterators`
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* Use `auto`
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* Use `auto`
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