Drake
OutputPort< T > Class Template Referenceabstract

An OutputPort belongs to a System and represents the properties of one of that System's output ports. More...

#include <drake/systems/framework/output_port.h>

Public Member Functions

 ~OutputPort () override
 
template<typename ValueType = Eigen::VectorBlock<const VectorX<T>>>
const ValueType & Eval (const Context< T > &context) const
 Returns a reference to the up-to-date value of this output port contained in the given Context. More...
 
std::unique_ptr< AbstractValueAllocate () const
 Allocates a concrete object suitable for holding the value to be exposed by this output port, and returns that as an AbstractValue. More...
 
void Calc (const Context< T > &context, AbstractValue *value) const
 Unconditionally computes the value of this output port with respect to the given context, into an already-allocated AbstractValue object whose concrete type must be exactly the same as the type returned by this port's allocator. More...
 
const System< T > & get_system () const
 Returns a reference to the System that owns this output port. More...
 
const AbstractValueEvalAbstract (const Context< T > &context) const
 (Deprecated.) More...
 
Eigen::VectorBlock< const VectorX< T > > EvalEigenVector (const Context< T > &context) const
 (Deprecated.) More...
 
const std::string & get_name () const
 Get port name. More...
 
std::string GetFullDescription () const
 Returns a verbose human-readable description of port. More...
 
OutputPortIndex get_index () const
 Returns the index of this output port within the owning System. More...
 
PortDataType get_data_type () const
 Returns the port data type. More...
 
int size () const
 Returns the fixed size expected for a vector-valued port. More...
 
DependencyTicket ticket () const
 (Advanced.) Returns the DependencyTicket for this port within the owning System. More...
 
Does not allow copy, move, or assignment
 OutputPort (const OutputPort &)=delete
 
OutputPortoperator= (const OutputPort &)=delete
 
 OutputPort (OutputPort &&)=delete
 
OutputPortoperator= (OutputPort &&)=delete
 
- Public Member Functions inherited from OutputPortBase
 ~OutputPortBase () override
 
OutputPortIndex get_index () const
 Returns the index of this output port within the owning System. More...
 
const std::string & get_name () const
 Get port name. More...
 
std::string GetFullDescription () const
 Returns a verbose human-readable description of port. More...
 
PortDataType get_data_type () const
 Returns the port data type. More...
 
int size () const
 Returns the fixed size expected for a vector-valued port. More...
 
DependencyTicket ticket () const
 (Advanced.) Returns the DependencyTicket for this port within the owning System. More...
 
 OutputPortBase (const OutputPortBase &)=delete
 
OutputPortBaseoperator= (const OutputPortBase &)=delete
 
 OutputPortBase (OutputPortBase &&)=delete
 
OutputPortBaseoperator= (OutputPortBase &&)=delete
 
- Public Member Functions inherited from PortBase
virtual ~PortBase ()
 
const std::string & get_name () const
 Get port name. More...
 
std::string GetFullDescription () const
 Returns a verbose human-readable description of port. More...
 
PortDataType get_data_type () const
 Returns the port data type. More...
 
int size () const
 Returns the fixed size expected for a vector-valued port. More...
 
DependencyTicket ticket () const
 (Advanced.) Returns the DependencyTicket for this port within the owning System. More...
 
 PortBase (const PortBase &)=delete
 
PortBaseoperator= (const PortBase &)=delete
 
 PortBase (PortBase &&)=delete
 
PortBaseoperator= (PortBase &&)=delete
 

Protected Member Functions

 OutputPort (const System< T > *system, SystemBase *system_base, std::string name, OutputPortIndex index, DependencyTicket ticket, PortDataType data_type, int size)
 Provides derived classes the ability to set the base class members at construction. More...
 
virtual std::unique_ptr< AbstractValueDoAllocate () const =0
 A concrete OutputPort must provide a way to allocate a suitable object for holding the runtime value of this output port. More...
 
virtual void DoCalc (const Context< T > &context, AbstractValue *value) const =0
 A concrete OutputPort must implement this method to calculate the value this output port should have, given the supplied Context. More...
 
virtual const AbstractValueDoEval (const Context< T > &context) const =0
 A concrete OutputPort must provide access to the current value of this output port stored within the given Context. More...
 
- Protected Member Functions inherited from OutputPortBase
 OutputPortBase (internal::SystemMessageInterface *owning_system, std::string name, OutputPortIndex index, DependencyTicket ticket, PortDataType data_type, int size)
 Provides derived classes the ability to set the base class members at construction. More...
 
virtual internal::OutputPortPrerequisite DoGetPrerequisite () const =0
 Concrete output ports must implement this to return the prerequisite dependency ticket for this port, which may be in the current System or one of its immediate child subsystems. More...
 
- Protected Member Functions inherited from PortBase
 PortBase (const char *kind_string, internal::SystemMessageInterface *owning_system, std::string name, int index, DependencyTicket ticket, PortDataType data_type, int size)
 Provides derived classes the ability to set the base class members at construction. More...
 
int get_int_index () const
 Returns the index of this port within the owning System (i.e., an InputPortIndex or OutputPortIndex, but as a bare integer). More...
 
internal::SystemMessageInterface & get_mutable_system_base ()
 Returns get_system_base(), but without the const. More...
 
template<typename ValueType >
const ValueType & PortEvalCast (const AbstractValue &abstract) const
 Pull a value of a given type from an abstract value or issue a nice message if the type is not correct. More...
 
template<typename ValueType , typename T >
const ValueType & PortEvalCast (const BasicVector< T > &basic) const
 Downcast a basic vector to a more specific subclass (e.g., as generated by //tools/vector_gen) or issue a nice message if the type is not correct. More...
 
template<typename ValueType >
const ValueType & ThrowBadCast (const AbstractValue &abstract) const
 Reports that the user provided a bad ValueType argument to Eval. More...
 
template<typename ValueType , typename T >
const ValueType & ThrowBadCast (const BasicVector< T > &basic) const
 Reports that the user provided a bad ValueType argument to Eval. More...
 
void ThrowBadCast (const std::string &value_typename, const std::string &eval_typename) const
 Reports that the user provided a bad ValueType argument to Eval. More...
 

Detailed Description

template<typename T>
class drake::systems::OutputPort< T >

An OutputPort belongs to a System and represents the properties of one of that System's output ports.

OutputPort objects are assigned OutputPortIndex values in the order they are declared; these are unique within a single System.

An output port can be considered a "window" into a System that permits controlled exposure of one of the values contained in that System's Context at run time. Input ports of other subsystems may be connected to an output port to construct system diagrams with carefully managed interdependencies.

The exposed value may be the result of an output computation, or it may simply expose some other value contained in the Context, such as the values of state variables. The Context handles caching of output port values and tracks dependencies to ensure that the values are valid with respect to their prerequisites. Leaf systems provide for the production of output port values, by computation or forwarding from other values within the associated leaf context. A diagram's output ports, on the other hand, are exported from output ports of its contained subsystems.

An output port's value is always stored as an AbstractValue, but we also provide special handling for output ports known to have numeric (vector) values. Vector-valued ports may specify a particular vector length, or may leave that to be determined at runtime.

OutputPort objects support three important operations:

  • Allocate() returns an object that can hold the port's value.
  • Calc() unconditionally computes the port's value.
  • Eval() updates a cached value if necessary.
Template Parameters
TThe vector element type, which must be a valid Eigen scalar.

Instantiated templates for the following kinds of T's are provided:

They are already available to link against in the containing library. No other values for T are currently supported.

Constructor & Destructor Documentation

◆ OutputPort() [1/3]

OutputPort ( const OutputPort< T > &  )
delete

◆ OutputPort() [2/3]

OutputPort ( OutputPort< T > &&  )
delete

◆ ~OutputPort()

~OutputPort ( )
overridedefault

◆ OutputPort() [3/3]

OutputPort ( const System< T > *  system,
SystemBase system_base,
std::string  name,
OutputPortIndex  index,
DependencyTicket  ticket,
PortDataType  data_type,
int  size 
)
protected

Provides derived classes the ability to set the base class members at construction.

See OutputPortBase::OutputPortBase() for the meaning of these parameters.

Precondition
The name must not be empty.
The system parameter must be the same object as the system_base parameter.

Member Function Documentation

◆ Allocate()

std::unique_ptr<AbstractValue> Allocate ( ) const

Allocates a concrete object suitable for holding the value to be exposed by this output port, and returns that as an AbstractValue.

The returned object will never be null. If Drake assertions are enabled (typically only in Debug builds), validates for a vector-valued port that the returned AbstractValue is actually a BasicVector-derived type and that it has an acceptable size.

Note
If this is a vector-valued port, the underlying type is Value<BasicVector<T>>; downcast to BasicVector<T> before downcasting to the specific BasicVector subclass.

◆ Calc()

void Calc ( const Context< T > &  context,
AbstractValue value 
) const

Unconditionally computes the value of this output port with respect to the given context, into an already-allocated AbstractValue object whose concrete type must be exactly the same as the type returned by this port's allocator.

If Drake assertions are enabled (typically only in Debug builds), validates that the given value has exactly the same concrete type as is returned by the Allocate() method.

◆ DoAllocate()

virtual std::unique_ptr<AbstractValue> DoAllocate ( ) const
protectedpure virtual

A concrete OutputPort must provide a way to allocate a suitable object for holding the runtime value of this output port.

The particulars may depend on values and types of objects in the given Context.

Returns
A unique_ptr to the new value-holding object as an AbstractValue.

◆ DoCalc()

virtual void DoCalc ( const Context< T > &  context,
AbstractValue value 
) const
protectedpure virtual

A concrete OutputPort must implement this method to calculate the value this output port should have, given the supplied Context.

The value may be determined by computation or by copying from a source value in the Context.

Parameters
contextA Context that has already been validated as compatible with the System whose output port this is.
valueA pointer that has already be validated as non-null and pointing to an object of the right type to hold a value of this output port.

◆ DoEval()

virtual const AbstractValue& DoEval ( const Context< T > &  context) const
protectedpure virtual

A concrete OutputPort must provide access to the current value of this output port stored within the given Context.

If the value is already up to date with respect to its prerequisites in context, no computation should be performed. Otherwise, the implementation should arrange for the value to be computed, typically but not necessarily by invoking DoCalc().

Parameters
contextA Context that has already been validated as compatible with the System whose output port this is.

◆ Eval()

const ValueType& Eval ( const Context< T > &  context) const

Returns a reference to the up-to-date value of this output port contained in the given Context.

This is the preferred way to obtain an output port's value since it will not be recalculated once up to date.

If the value is not already up to date with respect to its prerequisites, it will recalculate an up-to-date value before the reference is returned. The recalculation may be arbitrarily expensive, but Eval() is constant time and very fast if the value is already up to date.

Template Parameters
ValueTypeThe type of the const-reference returned by this method. When omitted, the return type is an Eigen::VectorBlock (this is only valid when this is a vector-valued port). For abstract ports, the ValueType either can be the declared type of the port (e.g., lcmt_iiwa_status), or else in advanced use cases can be AbstractValue to get the type-erased value.
Returns
reference to the up-to-date value; if a ValueType is provided, the return type is const ValueType&; if a ValueType is omitted, the return type is Eigen::VectorBlock<const VectorX<T>>.
Exceptions
std::exceptionif the port is not connected.
Precondition
The output port is vector-valued (when no ValueType is provided).
The output port is of type ValueType (when ValueType is provided).

◆ EvalAbstract()

const AbstractValue& EvalAbstract ( const Context< T > &  context) const

(Deprecated.)

Deprecated:
"Use Eval() instead."
This will be removed from Drake on or after "2019-06-01" .

◆ EvalEigenVector()

Eigen::VectorBlock<const VectorX<T> > EvalEigenVector ( const Context< T > &  context) const

(Deprecated.)

Deprecated:
"Use Eval() instead."
This will be removed from Drake on or after "2019-06-01" .

◆ get_data_type()

PortDataType get_data_type

Returns the port data type.

◆ get_index()

OutputPortIndex get_index

Returns the index of this output port within the owning System.

For a Diagram, this will be the index within the Diagram, not the index within the LeafSystem whose output port was forwarded.

◆ get_name()

const std::string& get_name

Get port name.

◆ get_system()

const System<T>& get_system ( ) const

Returns a reference to the System that owns this output port.

Note that for a diagram output port this will be the diagram, not the leaf system whose output port was forwarded.

◆ GetFullDescription()

std::string GetFullDescription

Returns a verbose human-readable description of port.

This is useful for error messages or debugging.

◆ operator=() [1/2]

OutputPort& operator= ( const OutputPort< T > &  )
delete

◆ operator=() [2/2]

OutputPort& operator= ( OutputPort< T > &&  )
delete

◆ size()

int size

Returns the fixed size expected for a vector-valued port.

Not meaningful for abstract-valued ports.

◆ ticket()

(Advanced.) Returns the DependencyTicket for this port within the owning System.


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