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1718 lines (1318 loc) · 49.1 KB
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/*
# class
TODO split this up.
*/
#include "common.hpp"
#include "no_base_no_member.hpp"
class Empty {};
/**
This class has a compiler supplied default constructor.
*/
class ImplicitDefaultCtor {
public:
int i;
std::string s;
};
/**
This class has no default constructor since another constructor was defined.
*/
class NoDefaultCtor {
public:
NoDefaultCtor(int i) : i(i) {}
int i;
};
/**
This class defines a default constructor since it will also provide a non default one.
*/
class ExplicitDefaultCtor {
public:
int i;
ExplicitDefaultCtor(){}
ExplicitDefaultCtor(int i) : i(i){}
};
/**
This class uses its default copy constructor and assign operator.
*/
class DefaultCopyAssignCtor {
public:
int i;
DefaultCopyAssignCtor() : i(0) {}
DefaultCopyAssignCtor(int i) : i(i) {}
};
/**
This politically incorrect clas does not implement the equality == operator.
*/
class NoEquality {
public:
NoEquality() : i(0) {}
int i;
};
#if __cplusplus >= 201103L
class CtorFromCtor {
public:
std::vector<int> v;
/**
This constructor does the default which is calling the parent's default constrctor before its own.
An error would be generated if the parent class has no defalt constructor.
*/
CtorFromCtor(int i) : v(1,i) {}
/**
This constructor calls another constructor with arguments before running its own.
*/
CtorFromCtor(int i, int j) : CtorFromCtor(i) {
v.push_back(j);
}
};
#endif
#if __cplusplus >= 201103L
/**
This class exemplifies the `= default` syntax.
*/
class DefaultKeyword {
public:
/**
This is an explicitly defaulted constructor.
*/
DefaultKeyword() = default;
/**
This is an explicitly defaulted copy constructor.
*/
DefaultKeyword(const DefaultKeyword&) = default;
/**
This is an explicitly defaulted assignment operator.
*/
DefaultKeyword & operator=(const DefaultKeyword&) = default;
~DefaultKeyword() = default;
// ERROR: Not possible because the default constructor must take no arguments.
//DefaultKeyword(int i) = default;
// With the default keyword it is possible to have other
// constructors besides the Implicitly defined constructor.
DefaultKeyword(int i, std::string s) : i(i), s(s) {}
/**
ERROR: Cannot default anything other than:
- constructors
- destructors
- copy
- assignment
*/
//void f() = default;
int i;
std::string s;
};
/**
This class exemplifies the `= delete` syntax.
*/
class DeleteKeyword {
public:
DeleteKeyword() = delete;
DeleteKeyword(int i) : i(i) {}
DeleteKeyword(const DeleteKeyword&) = delete;
DeleteKeyword & operator=(const DeleteKeyword&) = delete;
/**
With this, the code would compile, but it would not be possible
to create any instances of this class, since at some point the destructor
would have to be called!
*/
//~DeleteKeyword() = delete;
/* It is possible to delete any function. */
void f() = delete;
int i;
};
#endif
/**
This class has an implicit default constructor.
*/
class UniformInitializationImplicitCtor {
public:
int i;
int j;
};
/**
This class has an explicit default constructor,
and no constructor that takes 2 ints.
*/
class UniformInitializationExplicitCtor {
public:
int i;
int j;
UniformInitializationExplicitCtor() : i(0), j(0) {}
};
/**
This class has a constructor that takes 2 ints.
*/
class UniformInitializationCtor2 {
public:
int i;
int j;
UniformInitializationCtor2(int i, int j) : i(i), j(j+1) {}
bool operator==(const UniformInitializationCtor2& other) {return this->i == other.i && this->j == other.j;}
};
int UniformInitializationCtor2Func(UniformInitializationCtor2 o){
return o.i + o.j;
}
class UniformInitializationList {
public:
int i;
int j;
UniformInitializationList(int i, int j) : i(i), j(j+1) {}
UniformInitializationList(std::initializer_list<int> list){
i = *(list.begin());
j = *(list.begin() + 1);
}
};
class MemberConstructorTest {
public:
NoBaseNoMember0 member0;
NoBaseNoMember1 member1;
MemberConstructorTest(){callStack.push_back("MemberConstructorTest::MemberConstructorTest()");}
~MemberConstructorTest(){callStack.push_back("MemberConstructorTest::~MemberConstructorTest()");}
void method(){callStack.push_back("MemberConstructorTest::method()");}
};
class Member {
public:
Member(){callStack.push_back("Member::Member()");}
Member(int i){callStack.push_back("Member::Member(int)");}
~Member(){callStack.push_back("Member::~Member()");}
void method() {callStack.push_back("Member::method()");}
int i;
};
class Nested {
public:
Nested() { callStack.push_back("Nested::Nested()"); }
};
/*
# this
Magic value that points to the current object.
It is implemented by the compiler by passing `this` as the first argument
of every non-static function of the class.
This is noticeable when doing operator overload:
*/
class Base {
public:
/// Best to put typedefs on top of class so def will go for entire class.
typedef int NESTED_INT;
Base() : i(0), j(1) {
callStack.push_back("Base::Base()");
// BAD: same as list init, except if i is an object
// to keep uniform style, always use list init
//this->i=0;
//this->j=1;
// ERROR: ic is const. must be initialized in list initialization.
//ic=0;
// BAD: compiles but infinite loop!
//Base b;
}
/*
# Initialization list
Initialization lists have 4 main uses:
1) avoid calling member object constructor and copy separately
https://stackoverflow.com/questions/12927169/how-can-i-initialize-c-object-member-variables-in-the-constructor
2) initializing base classes with non default constructors
3) initializing const elements
4) initializing member references &
5) C++11 delegating constructors: call another constructor of the current class
*/
Base(int i, int j) : i(i), j(j) {
callStack.push_back("Base::Base(int, int)");
}
// ERROR: constructor cannot be virtual:
//virtual Base(float f){}
#if __cplusplus >= 201103L
/// C++11 initialize array/std containers in list initializtion.
Base(float f) : i(0), fs4{f,f,f,f}, vi{0,1,2,3} {
callStack.push_back("Base::Base(float)");
}
#endif
virtual ~Base() {
callStack.push_back("Base::~Base()");
}
void method() {
callStack.push_back("Base::method()");
int i = iAmbiguous;
}
void constMethod() const;
void constMethod(int *&) const;
void methodAmbiguous(){callStack.push_back("Base::methodAmbiguous()");}
// virtual: decides on runtime based on object type
// http://stackoverflow.com/questions/2391679/can-someone-explain-c-virtual-methods
virtual void virtualMethod(){callStack.push_back("Base::virtualMethod()");}
int i, j;
// ERROR: cannot initialize here.
//int initialized_outside_ctor = 0;
int iPublic;
int iAmbiguous;
int* is;
float fs4[4];
std::vector<int> vi;
mutable int mutableI;
// ERROR: statics can be changed in const functions by default.
//static mutable int staticMutableI;
/*
BAD every class must have an assigment operator.
But then, assigment does something like this->ic = other->ic
You could redefine the assigment, but still in your new definition ic cannot be changed.
<http://stackoverflow.com/questions/634662/non-static-const-member-cant-use-default-assignment-operator>
*/
/*
# member initialization outside of constructor
*/
const int iConstInit = 0;
// ERROR: non-integral type.
//const static float fConstStatic = 0.0;
const static Member member;
// OK: why ok?
const static Member member2;
//default constructor works
//const static NoBaseNoMember(1);
/*
ERROR: non integral type must be init outside.
why integral types are an exception:
<http://stackoverflow.com/questions/13697265/static-const-double-cannot-have-an-in-class-initializer-why-is-it-so>
*/
class Nested {
public:
Nested() {
callStack.push_back("Base::Nested::Nested()");
int i = privateStaticInt;
//you have private access
}
Member m;
};
class Nested2 {
public:
Nested2() {
callStack.push_back("Base::Nested2::Nested2()");
}
Nested innerIn;
//inner one
::Nested innerOut;
//outter one
};
protected:
int iProtected;
void fProtected(){callStack.push_back("Base::fProtected()");}
private:
int iPrivate;
void fPrivate(){callStack.push_back("Base::fPrivate()");}
const static int privateStaticInt = 1;
typedef int PRIVATE_NESTED_INT;
};
/*
# friend
Allow external functions and other classes to access private memebers of this class.
Friendship is not automatically reflexive nor transitive.
One case in which friendship may be unavoidable is for operator overload of operators which cannot
be class members and must be implemented as external functions such as `operator<<`.
This happens because of the nature of operators, which may force them to be implemented outside the class.
<http://www.cplusplus.com/doc/tutorial/inheritance/>
# friend and templates
Things get complicated when friends and template classes interact:
<http://publib.boulder.ibm.com/infocenter/lnxpcomp/v8v101/index.jsp?topic=%2Fcom.ibm.xlcpp8l.doc%2Flanguage%2Fref%2Ffriends_and_templates.htm>
*/
class FriendOfFriend;
class Friend {
public:
friend class FriendOfFriend;
Friend(int i) : i(i) {}
int getI(){return this->i;}
//this declaration says that `friendGetIPrivate(Base)` is a friend of this class.
//It will be defined outside the class.
friend int friendGetI(Friend f);
/* The same as friendGetI, but also defined inside the class. */
friend int friendGetIInnerDefine(Friend f) {
// ERROR: it is as if this were a friend external function, so there is no `this`.
//return this->i;
return f.i;
}
int getFriendI(FriendOfFriend f);
private:
int i;
void privateMethod(){};
};
/* cannot use the word friend here */
int friendGetI(Friend f){
// ERROR: this is a non-member function, so no `this`.
//return this->i;
return f.i;
}
class FriendOfFriend {
public:
FriendOfFriend(int i) : i(i) {}
int getFriendI(Friend f){return f.i;}
void callFriendPrivateMethod(Friend f){f.privateMethod();}
private:
int i;
};
// ERROR: friend used outside class.
//friend int friendGetI(Friend f){return f.i;}
// ERROR: not a friend because reflexivity is not automatic.
//int Friend::getFriendI(FriendOfFriend f) {return f.i;}
/*
# const method
Methods that cannot change the data of their object.
Inner workings: the hidden *this* pointer is downgraded to `const X*` when passing it to the function:
void method() const
becomes:
void method(const Class* this) const
instead of:
void method(Class* this) const
*/
void Base::constMethod() const {
// ERROR: cant assign member in const func.
//this->i = 2;
// ERROR: cant call non const method inside const method!
// as that method could change the object
//this->member.method();
// ERROR: cant assign member of a member in const method.
//this->member.i = 1;
/*
# mutable
OK
Mutable allows you to change it even in a const method.
Application to multithreading:
http://stackoverflow.com/questions/105014/does-the-mutable-keyword-have-any-purpose-other-than-allowing-the-variable-to
*/
this->mutableI = 1;
callStack.push_back("Base::constMethod()");
{
// ERROR: conversion from const Base* to Base*.
//Base* this2 = this;
const Base* this2const = this;
}
}
// ERROR must not ommit the const here either.
//void Base::constMethod () {}
/*
Cannot return a non const pointer from a const method, since this is const,
so all members are also const.
*/
void Base::constMethod(int *& ip) const {
// ERROR: invalid conversion.
//ip = &this->iPrivate;
}
// Must come outside
const Member Base::member2 = Member(1);
// ERROR: must be declared inside.
//int Base::k;
class BaseProtected {
public:
BaseProtected(){callStack.push_back("BaseProtected::BaseProtected()");}
BaseProtected(int i){callStack.push_back("BaseProtected::BaseProtected(int)");}
~BaseProtected(){callStack.push_back("BaseProtected::~BaseProtected()");}
};
class BasePrivate {
public:
BasePrivate(){callStack.push_back("BasePrivate::BasePrivate()");}
BasePrivate(int i){callStack.push_back("BasePrivate::BasePrivate(int)");}
~BasePrivate(){callStack.push_back("BasePrivate::~BasePrivate()");}
};
class Derived : private BasePrivate {};
class Class :
public Base,
// ERROR: duplicate.
//public Base,
// WARN: cannot use BasePrivate inside: ambiguous.
//public Derived,
protected BaseProtected,
private BasePrivate
{
public:
/*
Call base constructors first.
*/
Class() : i(0), z(1) {
callStack.push_back("Class::Class()");
}
Class(int i) : i(i), z(0) {
callStack.push_back("Class::Class(int)");
}
/*
Calls specific base constructors instead of default ones
another application os initialization lists.
*/
Class(int i, int z) : Base(i,z), BaseProtected(i), BasePrivate(i), i(i), z(z) {
callStack.push_back("Class::Class(int, int)");
}
// WARN: BaseAbstract will be init after TODO ?
//Class() : BaseAbstract(), Base(i,z), BaseProtected(i), BasePrivate(i), i(i), z(z)
//try catch in case base constructor can throw exceptions
Class(int i, int j, int z) try : Base(i,j), i(i), z(z) {
callStack.push_back("Class::Class(int, int, int)");
}
catch(const std::exception &e) {
throw e;
}
Class(Member m) : m(m) {
// BAD: m constructor would be called, but this is useless since we have already called it!
// to construct it before.
// This is an application of initialization constructors.
//this->m = m;
callStack.push_back("Class::Class(Member)");
}
/*
Copy constructor.
Classes already have this by default.
Useful to customize if class does dynamic allocation!
*/
Class(const Class& c) : i(c.i), z(c.z), m(c.m) {
callStack.push_back("Class::Class(Class)");
}
// Classes don't have constructors from base by default.
Class(const Base& b) : Base(b) {
callStack.push_back("Class::Class(Base)");
}
/*
Also calls Base destructor after
*/
~Class() { callStack.push_back("Class::~Class()"); }
// Called method overwriding.
void method() { callStack.push_back("Class::method()"); }
// OK.
template<class C=int>
void methodTemplate() {
callStack.push_back("Class::methodTemplate()");
}
int i;
int z;
Member m;
Nested nested;
//Base nested class visible from here
};
//nested
// OK: you can see the nested class from derived classes
class NestedDerived : Class::Nested{};
class Class2 : public Base {
public:
// OK: you can override the Nested class from the Base also
class Nested{};
};
class ClassCast {
ClassCast(Class c){}
};
// ERROR:
//ClassDefault::ClassDefault(int i=0){}
/*
Illustrates the copy and swap idiom and related concepts like move contruction.
*/
class CopyAndSwap {
public:
int *is;
std::size_t n;
CopyAndSwap(std::size_t n, int val) : n(n) {
is = new int[n];
for (std::size_t i = 0; i < n; ++i) {
is[i] = val;
}
}
~CopyAndSwap(){
delete[] is;
}
CopyAndSwap& operator=(const CopyAndSwap& rhs) {
delete[] is;
is = new int[rhs.n];
return *this;
}
CopyAndSwap(const CopyAndSwap& other) {
}
};
// Design patterns
// VisibleInnerIterable
/*
this is the best way I could find to make a member
iterable object such as a container available outside
design goal:
- to change container type, you only change a single typedef
difficulty:
- there is no `Iterator` interface that iterates over anything in the stdlib
for performance reasons.
By iterable understand somtehing that has an `::iterator`,
a `begin()` and an `end()` methods, like stl containers
*/
class VisibleInnerIterable {
public:
VisibleInnerIterable();
typedef std::vector<int> Iterable;
const Iterable& getIterable();
private:
Iterable iterable;
};
VisibleInnerIterable::VisibleInnerIterable() : iterable{0,1,2} {}
const VisibleInnerIterable::Iterable& VisibleInnerIterable::getIterable() {
return iterable;
}
int main() {
#if __cplusplus >= 201103L
/*
define class inside function
*/
{
// As of C++11, classes can be defined inside functions!
// This matches the behaviour for structs in C.
{
class C {};
}
// Template classes however cannot be defined in functions.
// Just think what should the compiler do in this case?
{
//template<class T> class C {};
}
}
#endif
/*
# Constructor
Called whenever object is created to initialize the object.
*/
{
/*
# Default constructors
http://en.cppreference.com/w/cpp/language/default_constructor
Constructor that takes no arguments.
Can be one explicitly created by the programmer:
all that matters is that it takes no arguments.
It is a good idea to always implement a default constructor,
since this is the only way arrays of fixed numbers of objects can be created before C++03
The concept of default constructor exists because there are
certain differences in syntax and behaviour when using default constructors,
for example:
- the most vexing parse only happens for default constructors.
- the default constructor can be is implicitly declared and defiend by the compiler.
There are other functions which are also defined by default:
https://en.wikipedia.org/wiki/Special_member_functions
# Implicily declared constructors
If no explicit constructor is declared,
the compiler automatically declares the following functions:
- default constructor
- copy constructor
- assignment constructor
- destructor
If any constructor is explicitly declared, even one taking multiple default args,
then *none* of the implicitly declared constructors are declared: that must be done manually.
# Trivial default constructor
# Implicily defined default constructor
If the implicitly-declared default constructor is not deleted
or trivial, it is defined (that is, a function body is generated
and compiled) by the compiler, and it has exactly the same effect
as a user-defined constructor with empty body and empty initializer list.
That is, it calls the default constructors of the bases
and of the non-static members of this class.
In particular, the IDDC does not do zero initialization on non-class members
such as `int`, so those have undefined values.
*/
{
// To call the default constructor, use this syntax
{
callStack.clear();
NoBaseNoMember c; //default constructor was called!
std::vector<std::string> expectedCallStack = {
"NoBaseNoMember::NoBaseNoMember()",
};
assert(callStack == expectedCallStack);
}
/*
The implicitly defined default constructor does not necessarily initialize member built-in types:
http://stackoverflow.com/questions/2417065/does-the-default-constructor-initialize-built-in-types
Class member default constructors however are called.
*/
{
ImplicitDefaultCtor o;
if (o.i != 0)
// undefined behaviour.
std::cout << "ImplicitDefaultCtor undefined behaviour: o.i = " << o.i << std::endl;
// Defined behaviour because class:
assert(o.s == "");
// *however*, the following does value initialization,
// not the default constructor, and built-in members are indeed 0 initialized!
{
ImplicitDefaultCtor o = ImplicitDefaultCtor();
assert(o.i == 0);
}
}
{
// ERROR:
//NoDefaultCtor o;
// ERROR cannot be done because this class has not default constructors.
//NoDefaultCtor os[2];
// Implicit copy and assign are still defined:
NoDefaultCtor o(1);
NoDefaultCtor o2(o);
o = o2;
}
#if __cplusplus >= 201103L
/*
# Default keyword
As of C++11, the `= default` statement can be added to a constructor to explicitly
say that the default should be used.
This allows a class to have multple constructors,
plus the implictly defined one.
*/
{
DefaultKeyword o;
// Undefined behaviour.
//assert(o.i == 0);
assert(o.s == std::string());
o = DefaultKeyword(1, "a");
assert(o.i == 1);
assert(o.s == "a");
}
/*
# delete keyword
*/
{
// ERROR: Explicitly deleted:
//DeleteKeyword o;
DeleteKeyword o(1);
// ERROR: Explicitly deleted:
//DeleteKeyword o2(o);
DeleteKeyword o2(2);
// ERROR: Explicitly deleted:
//o2 = o1;
}
#endif
}
/*
Value initialization and zero initialization are both a bit subtle,
so it is best not to rely on them.
C++ has 3 types of init
# Default initialization
# Value initialization
# Zero initialization
- http://en.cppreference.com/w/cpp/language/value_initialization
- http://en.cppreference.com/w/cpp/language/zero_initialization
- http://stackoverflow.com/questions/1613341/what-do-the-following-phrases-mean-in-c-zero-default-and-value-initializat
# Aggregate initialization
http://en.cppreference.com/w/cpp/language/aggregate_initialization
# POD
Plain old data:
http://stackoverflow.com/questions/4178175/what-are-aggregates-and-pods-and-how-why-are-they-special
*/
{
// Syntax with new.
{
// Base types.
{
int* is = new int[2]();
assert(is[0] == 0);
assert(is[1] == 0);
delete[] is;
}
// Works for structs.
{
struct T {int a;};
T *t = new T[1]();
assert(t[0].a == 0);
delete[] t;
}
/*
Works for objects.
Note how the default constructor was called since `z == 1`.
*/
{
{
Class *cs = new Class[1]();
assert(cs[0].i == 0);
assert(cs[0].z == 1);
delete[] cs;
}
}
// But only works with default constructors.
{
//Class *cs = new [1](1);
}
}
}
/*
# initialize built-in types
http://stackoverflow.com/questions/5113365/do-built-in-types-have-default-constructors
C++ adds new ways to initialize base types.
Those are not however constructors.
They probably just mimic constructor syntax to help blurr the distinction
between built-in types and classes and make templates and typedefs work better.
*/
{
// Parenthesis initialization
{
int i(1);
assert(i == 1);
}
{
// Most vexing parse.
//int i();
}
{
int i = int();
assert(i == 0);
}
#if __cplusplus >= 201103L
/*
# Brace initialization of scalars
See uniform initialization.
<http://stackoverflow.com/questions/14232184/initializing-scalars-with-braces>
# Uniform initialization
In c++11 every type can be initialized consistently with `{}`.