SLIDE 1
Initializer lists Uniform initialization
Initializer lists Uniform initialization
Initializer lists
- myClass : myInt(1), myContainer() ...
Initializer lists and uniform initialization slides based on talk - - PowerPoint PPT Presentation
Initializer lists and uniform initialization slides based on talk - - PowerPoint PPT Presentation
Initializer lists Uniform initialization Initializer lists and uniform initialization slides based on talk by Bjarne Stroustrup Jon Elverkilde April 25, 2008 Initializer lists Uniform initialization Initializer lists myClass :
SLIDE 2
SLIDE 3
Initializer lists Uniform initialization
Initializer lists
- myClass : myInt(1), myContainer() ...
- int my array[] = { 1,2,3 };
SLIDE 4
Initializer lists Uniform initialization
C and C++ style initialization
C style:
- X a = {v};
- X a = v;
C++ additions:
- new X(v);
- X a(v);
- X(v);
SLIDE 5
Initializer lists Uniform initialization
What’s the problem?
Consider the task of initializing a vector with the values 1,2,3:
- 1. std::vector<int> v;
SLIDE 6
Initializer lists Uniform initialization
What’s the problem?
Consider the task of initializing a vector with the values 1,2,3:
- 1. std::vector<int> v;
- 2. v.push back(1);
SLIDE 7
Initializer lists Uniform initialization
What’s the problem?
Consider the task of initializing a vector with the values 1,2,3:
- 1. std::vector<int> v;
- 2. v.push back(1);
- 3. v.push back(2);
SLIDE 8
Initializer lists Uniform initialization
What’s the problem?
Consider the task of initializing a vector with the values 1,2,3:
- 1. std::vector<int> v;
- 2. v.push back(1);
- 3. v.push back(2);
- 4. v.push back(3);
SLIDE 9
Initializer lists Uniform initialization
What’s the problem?
Now consider the array:
- int my array[] = { 1,2,3 };
- That’s not fair!
- and it violates a fundamental design principle: “provide as
good support for user-defined types as for built-in types”.
SLIDE 10
Initializer lists Uniform initialization
What’s the problem?
Now consider the array:
- int my array[] = { 1,2,3 };
- That’s not fair!
- and it violates a fundamental design principle: “provide as
good support for user-defined types as for built-in types”.
- So this is what we get:
- vector<int> v = { 1,2,3 };
- template<class T> sum(const vector<T> &);
- int x = sum({ 1,2,3 });
SLIDE 11
Initializer lists Uniform initialization
How?
- provide basic type initializer list<T>
- classes can provide initializer list-constructor
SLIDE 12
Initializer lists Uniform initialization
How?
- provide basic type initializer list<T>
- classes can provide initializer list-constructor
When {} is used:
- 1. Check for initializer list-constructor
- 2. Check for normal constructor
- 3. Check C-style (array, struct)
SLIDE 13
Initializer lists Uniform initialization
Uniform initialization
Different syntaxes mean different things:
- X t1 = v;
- X t2(v);
- X t3 = {v};
- X t4 = X(v);
X and v can be chosen so that 0,1,2,3 or 4 of these compile.
SLIDE 14
Initializer lists Uniform initialization
Solution
With initializer lists:
- X x1 = X{ 1,2 };
- X x2 = { 1,2 };
- X x3{ 1,2 };
- X* p2 = new X{ 1,2 };
These all mean initialize X with initializer list { 1,2 }.
SLIDE 15
Initializer lists Uniform initialization
Sources
This presentation was based on a (1 hour) Google Talk by Bjarne Stroustrup: http://video.google.com/videoplay?docid= 5262479012306588324
- r find at Stroustrup’s site (bottom):