diff --git a/CppCoreGuidelines.md b/CppCoreGuidelines.md index 1c92c21..b769119 100644 --- a/CppCoreGuidelines.md +++ b/CppCoreGuidelines.md @@ -3165,7 +3165,7 @@ The language guarantees that a `T&` refers to an object, so that testing for `nu ##### Example - class car + class Car { array w; // ... @@ -3176,7 +3176,7 @@ The language guarantees that a `T&` refers to an object, so that testing for `nu void use() { - car c; + Car c; wheel& w0 = c.get_wheel(0); // w0 has the same lifetime as c } @@ -3407,7 +3407,7 @@ It's confusing. Writing `[=]` in a member function appears to capture by value, ##### Example - class myclass { + class My_class { int x = 0; // ... @@ -5547,28 +5547,28 @@ Worse, a direct or indirect call to an unimplemented pure virtual function from ##### Example, bad - class base { + class Base { public: virtual void f() = 0; // not implemented - virtual void g(); // implemented with base version - virtual void h(); // implemented with base version + virtual void g(); // implemented with Base version + virtual void h(); // implemented with Base version }; - class derived : public base { + class Derived : public Base { public: - void g() override; // provide derived implementation - void h() final; // provide derived implementation + void g() override; // provide Derived implementation + void h() final; // provide Derived implementation - derived() + Derived() { // BAD: attempt to call an unimplemented virtual function f(); - // BAD: will call derived::g, not dispatch further virtually + // BAD: will call Derived::g, not dispatch further virtually g(); // GOOD: explicitly state intent to call only the visible version - derived::g(); + Derived::g(); // ok, no qualification needed, h is final h(); @@ -5906,10 +5906,10 @@ Interfaces should normally be composed entirely of public pure virtual functions ##### Example - class my_interface { + class My_interface { public: // ...only pure virtual functions here ... - virtual ~my_interface() {} // or =default + virtual ~My_interface() {} // or =default }; ##### Example, bad @@ -6284,19 +6284,19 @@ Copying a base is usually slicing. If you really need copy semantics, copy deepl ##### Example - class base { + class Base { public: - virtual owner clone() = 0; - virtual ~base() = 0; + virtual owner clone() = 0; + virtual ~Base() = 0; - base(const base&) = delete; - base& operator=(const base&) = delete; + Base(const Base&) = delete; + Base& operator=(const Base&) = delete; }; - class derived : public base { + class Derived : public Base { public: - owner clone() override; - virtual ~derived() override; + owner clone() override; + virtual ~Derived() override; }; Note that because of language rules, the covariant return type cannot be a smart pointer. See also [C.67](#Rc-copy-virtual). @@ -6314,11 +6314,11 @@ A trivial getter or setter adds no semantic value; the data item could just as w ##### Example - class point { + class Point { int x; int y; public: - point(int xx, int yy) : x{xx}, y{yy} { } + Point(int xx, int yy) : x{xx}, y{yy} { } int get_x() { return x; } void set_x(int xx) { x = xx; } int get_y() { return y; } @@ -6328,7 +6328,7 @@ A trivial getter or setter adds no semantic value; the data item could just as w Consider making such a class a `struct` -- that is, a behaviorless bunch of variables, all public data and no member functions. - struct point { + struct Point { int x = 0; int y = 0; }; @@ -6562,18 +6562,18 @@ That can cause confusion: An overrider do not inherit default arguments. ##### Example, bad - class base { + class Base { public: virtual int multiply(int value, int factor = 2) = 0; }; - class derived : public base { + class Derived : public Base { public: int multiply(int value, int factor = 10) override; }; - derived d; - base& b = d; + Derived d; + Base& b = d; b.multiply(10); // these two calls will call the same function but d.multiply(10); // with different arguments and so different results @@ -11984,7 +11984,7 @@ The same applies almost as strongly to member variables, for the same reason. // etc. } - class mytype { + class My_type { volatile int i = 0; // suspicious, volatile member variable // etc. }; @@ -12171,12 +12171,12 @@ Not all member functions can be called. ##### Example - class vector { // very simplified vector of doubles + class Vector { // very simplified vector of doubles // if elem!=nullptr then elem points to sz doubles public: - vector() : elem{nullptr}, sz{0}{} + Vector() : elem{nullptr}, sz{0}{} vctor(int s) : elem{new double},sz{s} { /* initialize elements */ } - ~vector() { delete elem; } + ~Vector() { delete elem; } double& operator[](int s) { return elem[s]; } // ... @@ -13279,7 +13279,7 @@ It also avoids brittle or inefficient workarounds. Convention: That's the way th int sz; }; - vector v(10); + Vector v(10); v[7] = 9.9; ##### Example, bad @@ -14032,7 +14032,7 @@ They can also be used to wrap a trait. ##### Example template - class matrix { + class Matrix { // ... using Iterator = typename std::vector::iterator; // ... @@ -15103,31 +15103,31 @@ Of course, range-for is better still where it does what you want. Use the least-derived class that has the functionality you need. - class base { + class Base { public: void f(); void g(); }; - class derived1 : public base { + class Derived1 : public Base { public: void h(); }; - class derived2 : public base { + class Derived2 : public Base { public: void j(); }; - // bad, unless there is a specific reason for limiting to derived1 objects only - void myfunc(derived1& param) + // bad, unless there is a specific reason for limiting to Derived1 objects only + void myfunc(Derived1& param) { use(param.f()); use(param.g()); } - // good, uses only base interface so only commit to that - void myfunc(base& param) + // good, uses only Base interface so only commit to that + void myfunc(Base& param) { use(param.f()); use(param.g()); @@ -16051,21 +16051,21 @@ Use of these casts can violate type safety and cause the program to access a var ##### Example, bad - class base { public: virtual ~base() = 0; }; + class Base { public: virtual ~Base() = 0; }; - class derived1 : public base { }; + class Derived1 : public Base { }; - class derived2 : public base { + class Derived2 : public Base { std::string s; public: std::string get_s() { return s; } }; - derived1 d1; - base* p = &d1; // ok, implicit conversion to pointer to base is fine + Derived1 d1; + Base* p = &d1; // ok, implicit conversion to pointer to Base is fine - // BAD, tries to treat d1 as a derived2, which it is not - derived2* p2 = static_cast(p); + // BAD, tries to treat d1 as a Derived2, which it is not + Derived2* p2 = static_cast(p); // tries to access d1's nonexistent string member, instead sees arbitrary bytes near d1 cout << p2->get_s(); @@ -16120,31 +16120,31 @@ Casting away `const` is a lie. If the variable is actually declared `const`, it' Sometimes you may be tempted to resort to `const_cast` to avoid code duplication, such as when two accessor functions that differ only in `const`-ness have similar implementations. For example: - class bar; + class Bar; - class foo { - bar mybar; + class Foo { + Bar mybar; public: // BAD, duplicates logic - bar& get_bar() { + Bar& get_bar() { /* complex logic around getting a non-const reference to mybar */ } - const bar& get_bar() const { + const Bar& get_bar() const { /* same complex logic around getting a const reference to mybar */ } }; Instead, prefer to share implementations. Normally, you can just have the non-`const` function call the `const` function. However, when there is complex logic this can lead to the following pattern that still resorts to a `const_cast`: - class foo { - bar mybar; + class Foo { + Bar mybar; public: // not great, non-const calls const version but resorts to const_cast - bar& get_bar() { - return const_cast(static_cast(*this).get_bar()); + Bar& get_bar() { + return const_cast(static_cast(*this).get_bar()); } - const bar& get_bar() const { + const Bar& get_bar() const { /* the complex logic around getting a const reference to mybar */ } }; @@ -16153,16 +16153,16 @@ Although this pattern is safe when applied correctly, because the caller must ha Instead, prefer to put the common code in a common helper function -- and make it a template so that it deduces `const`. This doesn't use any `const_cast` at all: - class foo { - bar mybar; + class Foo { + Bar mybar; template // good, deduces whether T is const or non-const static auto get_bar_impl(T& t) -> decltype(t.get_bar()) { /* the complex logic around getting a possibly-const reference to mybar */ } public: // good - bar& get_bar() { return get_bar_impl(*this); } - const bar& get_bar() const { return get_bar_impl(*this); } + Bar& get_bar() { return get_bar_impl(*this); } + const Bar& get_bar() const { return get_bar_impl(*this); } }; **Exception**: You may need to cast away `const` when calling `const`-incorrect functions. Prefer to wrap such functions in inline `const`-correct wrappers to encapsulate the cast in one place. @@ -16183,21 +16183,21 @@ Note that a C-style `(T)expression` cast means to perform the first of the follo std::string s = "hello world"; double* p = (double*)(&s); // BAD - class base { public: virtual ~base() = 0; }; + class Base { public: virtual ~Base() = 0; }; - class derived1 : public base { }; + class Derived1 : public Base { }; - class derived2 : public base { + class Derived2 : public Base { std::string s; public: std::string get_s() { return s; } }; - derived1 d1; - base* p = &d1; // ok, implicit conversion to pointer to base is fine + Derived1 d1; + Base* p = &d1; // ok, implicit conversion to pointer to Base is fine - // BAD, tries to treat d1 as a derived2, which it is not - derived2* p2 = (derived2*)(p); + // BAD, tries to treat d1 as a Derived2, which it is not + Derived2* p2 = (Derived2*)(p); // tries to access d1's nonexistent string member, instead sees arbitrary bytes near d1 cout << p2->get_s(); @@ -17487,27 +17487,27 @@ Should destruction behave virtually? That is, should destruction through a point The common case for a base class is that it's intended to have publicly derived classes, and so calling code is just about sure to use something like a `shared_ptr`: - class base { + class Base { public: - ~base(); // BAD, not virtual - virtual ~base(); // GOOD + ~Base(); // BAD, not virtual + virtual ~Base(); // GOOD // ... }; - class derived : public base { /* ... */ }; + class Derived : public Base { /* ... */ }; { - unique_ptr pb = make_unique(); + unique_ptr pb = make_unique(); // ... - } // ~pb invokes correct destructor only when ~base is virtual + } // ~pb invokes correct destructor only when ~Base is virtual In rarer cases, such as policy classes, the class is used as a base class for convenience, not for polymorphic behavior. It is recommended to make those destructors protected and nonvirtual: - class my_policy { + class My_policy { public: - virtual ~my_policy(); // BAD, public and virtual + virtual ~My_policy(); // BAD, public and virtual protected: - ~my_policy(); // GOOD + ~My_policy(); // GOOD // ... }; @@ -17523,7 +17523,7 @@ For a base class `Base`, calling code might try to destroy derived objects throu To write a base class is to define an abstraction (see Items 35 through 37). Recall that for each member function participating in that abstraction, you need to decide: * Whether it should behave virtually or not. -* Whether it should be publicly available to all callers using a pointer to Base or else be a hidden internal implementation detail. +* Whether it should be publicly available to all callers using a pointer to `Base` or else be a hidden internal implementation detail. As described in Item 39, for a normal member function, the choice is between allowing it to be called via a pointer to `Base` nonvirtually (but possibly with virtual behavior if it invokes virtual functions, such as in the NVI or Template Method patterns), virtually, or not at all. The NVI pattern is a technique to avoid public virtual functions. @@ -17560,51 +17560,51 @@ Never allow an error to be reported from a destructor, a resource deallocation f ##### Example - class nefarious { + class Nefarious { public: - nefarious() { /* code that could throw */ } // ok - ~nefarious() { /* code that could throw */ } // BAD, should not throw + Nefarious() { /* code that could throw */ } // ok + ~Nefarious() { /* code that could throw */ } // BAD, should not throw // ... }; -1. `nefarious` objects are hard to use safely even as local variables: +1. `Nefarious` objects are hard to use safely even as local variables: void test(string& s) { - nefarious n; // trouble brewing + Nefarious n; // trouble brewing string copy = s; // copy the string } // destroy copy and then n Here, copying `s` could throw, and if that throws and if `n`'s destructor then also throws, the program will exit via `std::terminate` because two exceptions can't be propagated simultaneously. -2. Classes with `nefarious` members or bases are also hard to use safely, because their destructors must invoke `nefarious`' destructor, and are similarly poisoned by its poor behavior: +2. Classes with `Nefarious` members or bases are also hard to use safely, because their destructors must invoke `Nefarious`' destructor, and are similarly poisoned by its poor behavior: - class innocent_bystander { - nefarious member; // oops, poisons the enclosing class's destructor + class Innocent_bystander { + Nefarious member; // oops, poisons the enclosing class's destructor // ... }; void test(string& s) { - innocent_bystander i; // more trouble brewing + Innocent_bystander i; // more trouble brewing string copy2 = s; // copy the string } // destroy copy and then i Here, if constructing `copy2` throws, we have the same problem because `i`'s destructor now also can throw, and if so we'll invoke `std::terminate`. -3. You can't reliably create global or static `nefarious` objects either: +3. You can't reliably create global or static `Nefarious` objects either: - static nefarious n; // oops, any destructor exception can't be caught + static Nefarious n; // oops, any destructor exception can't be caught -4. You can't reliably create arrays of `nefarious`: +4. You can't reliably create arrays of `Nefarious`: void test() { - std::array arr; // this line can std::terminate(!) + std::array arr; // this line can std::terminate(!) } The behavior of arrays is undefined in the presence of destructors that throw because there is no reasonable rollback behavior that could ever be devised. Just think: What code can the compiler generate for constructing an `arr` where, if the fourth object's constructor throws, the code has to give up and in its cleanup mode tries to call the destructors of the already-constructed objects ... and one or more of those destructors throws? There is no satisfactory answer. @@ -17612,9 +17612,9 @@ Never allow an error to be reported from a destructor, a resource deallocation f 5. You can't use `Nefarious` objects in standard containers: - std::vector vec(10); // this line can std::terminate() + std::vector vec(10); // this line can std::terminate() - The standard library forbids all destructors used with it from throwing. You can't store `nefarious` objects in standard containers or use them with any other part of the standard library. + The standard library forbids all destructors used with it from throwing. You can't store `Nefarious` objects in standard containers or use them with any other part of the standard library. ##### Note @@ -17658,20 +17658,20 @@ If you define a move constructor, you must also define a move assignment operato ##### Example - class x { + class X { // ... public: - x(const x&) { /* stuff */ } + X(const X&) { /* stuff */ } // BAD: failed to also define a copy assignment operator - x(x&&) { /* stuff */ } + X(x&&) { /* stuff */ } // BAD: failed to also define a move assignment operator }; - x x1; - x x2 = x1; // ok + X x1; + X x2 = x1; // ok x2 = x1; // pitfall: either fails to compile, or does something suspicious If you define a destructor, you should not use the compiler-generated copy or move operation; you probably need to define or suppress copy and/or move. @@ -17690,20 +17690,20 @@ If you define a destructor, you should not use the compiler-generated copy or mo If you define copying, and any base or member has a type that defines a move operation, you should also define a move operation. - class x { + class X { string s; // defines more efficient move operations // ... other data members ... public: - x(const x&) { /* stuff */ } - x& operator=(const x&) { /* stuff */ } + X(const X&) { /* stuff */ } + X& operator=(const X&) { /* stuff */ } - // BAD: failed to also define a move construction and move assignment - // (why wasn't the custom "stuff" repeated here?) + // BAD: failed to also define a move construction and move assignment + // (why wasn't the custom "stuff" repeated here?) }; - x test() + X test() { - x local; + X local; // ... return local; // pitfall: will be inefficient and/or do the wrong thing }