Regular type vs view type¶
A fundamental distinction in TRIQS is the difference between the regular type and the corresponding view types.
The regular types
Following the definition of A. Stepanov, a regular type is a value, much like an int, a double, or a std::vector. Cf http://www.stepanovpapers.com/DeSt98.pdf (I added move semantics to the definition).
It has value semantics, more precisely
T a; // default constructible T a = b; T a (b); // copy constructible a = b; // assignment a == b; a != b; // Equality.
with the following properties
T a = b; assert(a==b); T a; a=b; is equivalent to T a=b; T a=c; T b=c; a=d; assert(b==c);
When copied, assigned, it makes deep copy of the data and resizes itself if necessary (like e.g. std::vector).
Examples:
 std::vector<T>
 triqs::arrays::array<T,R>, triqs::arrays::matrix<T>, triqs::arrays::vector<T>
The view types
 They have a reference semantics.
 They are just partial or complete views of the corresponding regular type.
 They never make deep copy, either in copying, constructing, transforming to python,
 They cannot be resized.
 They are useful to work on arrays, matrices, or on some part thereof, without making copies (e.g. on a slice of an array, a column of a matrix).
 Examples:
 triqs::arrays::array_view<T,R>, triqs::arrays::matrix_view, triqs::arrays::vector_view<T>
Many triqs containers (array, matrix, green functions) is therefore provided in two flavors, and it is crucial for the user to learn and understand their difference in order to use them appropriately.
Behaviour comparison table between regular and view types¶
A detailed comparison of the behaviour of the two type of types is provided in the following table.
Topics  regular type (e.g. array, matrix, vector)  view type (e.g. array_view, matrix_view, vector_view) 

Contructors 


Default Contructor 


Copy contructors 


Assignment (=) 


Resizing 


Invalidation 


Data Contiguity 

