mirror of
https://github.com/triqs/dft_tools
synced 2024-11-01 03:33:50 +01:00
92 lines
3.5 KiB
ReStructuredText
92 lines
3.5 KiB
ReStructuredText
.. highlight:: c
|
|
|
|
Assignment
|
|
=========================
|
|
|
|
The `value classes` and the `view classes` have a quite general assignment operator (=),
|
|
and corresponding compound operators (+=, -=).
|
|
We will illustrate it on the `array` class, it is the same for `matrix` and `vector`.
|
|
|
|
Assignment operator (=)
|
|
-------------------------------------------------
|
|
|
|
The `value classes` and the `view classes` have a quite general assignment operator.
|
|
|
|
* **Syntax** : the syntax is the same in both cases::
|
|
|
|
template<typename RHS> array & operator=(const RHS & X);
|
|
template<typename RHS> array_view & operator=(const RHS & X);
|
|
|
|
* **What can be RHS ?**
|
|
|
|
RHS can be ... anything that models the HasImmutableArrayInterface concept !
|
|
|
|
e.g. : array, array_view, matrix, matrix_view,
|
|
but also formal expression (See , e.g. A+B), or any custom object of your choice.
|
|
|
|
* **Behaviour**
|
|
|
|
================= ======================================================================= ======================================================================================
|
|
Topic value class : array, matrix, vector view: array_view, matrix_view, vector_view
|
|
================= ======================================================================= ======================================================================================
|
|
RHS ... - RHS models the concept `HasImmutableArrayInterface`. - RHS models HasImmutableArrayInterface
|
|
[or less ? : RHS can be evaluated in the domain_type::value_type, no domain needed.].
|
|
Effect - array is resized to have a domain X.domain() - View's domain must match X's domain or behaviour is undefined.
|
|
- array is filled with the evaluation of X. - array is filled with the evaluation of X.
|
|
================= ======================================================================= ======================================================================================
|
|
|
|
* By evaluation of X, we mean :
|
|
|
|
- a copy if X is an array.
|
|
- computing the value if X is an expression.
|
|
|
|
* **Optimisation** `[advanced]`
|
|
|
|
In some case, we know that optimisation is possible.
|
|
If the RHS class derives from `Tag::has_special_assign`, then the instruction ::
|
|
|
|
A = rhs;
|
|
|
|
will be rewritten by compiler as ::
|
|
|
|
rhs.assign_invoke(A);
|
|
|
|
An example is the matmul class, which stores the ref. to the objects to be multiplied.
|
|
If A and B are matrices, writing ::
|
|
|
|
C = matmul(A,B); // (1)
|
|
|
|
is rewritten as ::
|
|
|
|
matmul(A,B).assign_invoke(C);
|
|
|
|
which is then itself rewritten into (without all the messy details) ::
|
|
|
|
call_lapack( A, B, C); // (2)
|
|
|
|
The point is that :
|
|
|
|
* the user code is (1), very simple and readable
|
|
* but the compiler compiles (2), which eliminates temporaries...
|
|
|
|
|
|
Compound operators (+=, -=, * =, /=)
|
|
-------------------------------------------------
|
|
|
|
|
|
* **Syntax**
|
|
|
|
The syntax is natural ::
|
|
|
|
template<typename RHS> array & operator += (const RHS & X);
|
|
template<typename RHS> array & operator -= (const RHS & X);
|
|
template<typename RHS> array & operator *= (const Scalar & S);
|
|
template<typename RHS> array & operator /= (const Scalar & S);
|
|
|
|
* **Behaviour**
|
|
|
|
- Domain must match.
|
|
- X is evaluated and added term by term.
|
|
|
|
To be written : special operators.
|