operations_research::BaseIntExpr Class Reference

This is the base class for all expressions that are not variables. More...

#include <constraint_solveri.h>

Inheritance diagram for operations_research::BaseIntExpr:

List of all members.

Public Member Functions
	BaseIntExpr (Solver *const s)
virtual	~BaseIntExpr ()
virtual IntVar *	Var ()
	Creates a variable from the expression.
virtual IntVar *	CastToVar ()

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Detailed Description

This is the base class for all expressions that are not variables.

It proposes a basic 'CastToVar()' implementation. The class of expressions represent two types of objects: variables and subclasses of BaseIntExpr. Variables are stateful objects that provide a rich API (remove values, WhenBound...). On the other hand, subclasses of BaseIntExpr represent range-only stateless objects. That is the min(A + B) is recomputed each time as min(A) + min(B). Furthermore, sometimes, the propagation on an expression is not complete, and Min(), Max() are not monononic with respect to SetMin() and SetMax(). For instance, A is a var with domain [0 .. 5], and B another variable with domain [0 .. 5]. Then Plus(A, B) has domain [0, 10]. If we apply SetMax(Plus(A, B), 4)). Then we will deduce that both A and B will have domain [0 .. 4]. In that case, Max(Plus(A, B)) is 8 and not 4. To get back monotonicity, we will 'cast' the expression into a variable using the Var() method (that will call CastToVar() internally). The resulting variable will be stateful and monotonic.

Finally, one should never store a pointer to a IntExpr, or BaseIntExpr in the code. The safe code should always call Var() on an expression built by the solver, and store the object as an IntVar*. This is a consequence of the stateless nature of the expressions that makes the code error-prone.

Definition at line 111 of file constraint_solveri.h.

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Constructor & Destructor Documentation

operations_research::BaseIntExpr::BaseIntExpr

(

Solver *const

s

)

[inline, explicit]

Definition at line 113 of file constraint_solveri.h.

virtual operations_research::BaseIntExpr::~BaseIntExpr

(

)

[inline, virtual]

Definition at line 114 of file constraint_solveri.h.

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Member Function Documentation

IntVar * operations_research::BaseIntExpr::Var

(

)

[virtual]

Creates a variable from the expression.

Implements operations_research::IntExpr.

Definition at line 5031 of file expressions.cc.

IntVar * operations_research::BaseIntExpr::CastToVar

(

)

[virtual]

Definition at line 5039 of file expressions.cc.

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The documentation for this class was generated from the following files:

• or-tools/src/constraint_solver/constraint_solveri.h
• or-tools/src/constraint_solver/expressions.cc