GlishValue.h

Classes

GlishValue -- holds any type of Glish value (full description)

Global Functions -- output GlishValue to an ostream (in ASCII) (full description)

class GlishValue

Types

enum ValueType

ARRAY

RECORD

Interface

Public Members

GlishValue()

GlishValue(Value *value, Bool copy=False)

GlishValue(const GlishValue &other)

virtual ~GlishValue()

GlishValue &operator=(const GlishValue &other)

void addAttribute(const String &name, const GlishValue &value)

Bool attributeExists(const String &name) const

GlishValue getAttribute(const String &name) const

ValueType type() const

uInt nelements() const

String format(uInt maxArrayLength=10) const

virtual Bool ok() const

const Value *value() const

Bool isUnset() const

static const GlishRecord& getUnset()

Protected Members

void copyset(const Value *value)

Private Members

Bool isUnsetPriv() const

Description

Review Status

Reviewed By:

pshannon

Date Reviewed:

1994/10/28

Programs:

Demos:

• dGlish

Prerequisite

• It is probably helpful to understand Glish values in a general way. The whole point of this class though is to hide the details! This Glish User manual has a chapter on the Glish client library where the Glish Value class is described.

Synopsis

Copy-on-write means that when a copy or an assignment is made, a physical copy is not made, the representation is shared via a pointer. However when one of the copies is changed, a physical copy is first made. So, basically this technique avoids the physical copy for as long as possible, in the hope that it might never be needed.

1. The ability to add or remove attributes (a named GlishValue) to this GlishValue.
2. The ability to get a formatted string representation of this value (or use a Glish value with an iostream).

Additionally, various inquiry functions are provided, for example to determine whether this value is an array or a record, and to say how long it is.

Example

Motivation

For the morbidly curious, here's an example of how one would turn an AIPS++ Array into a native Glish Value object if these wrapper classes did not exist.

    Array<Complex ac = ...;
    
    // Get the values from the AIPS++ array
    Bool del;
    Complex *aipsComplexPtr = ac.getStorage(del);
    
    // Create a receptor array note that complex != Complex!!
    complex *glishComplexPtr = new complex[ac.nelements()];
    if ((glishComplexPtr) == 0) { ... memory error ...}
    
    // Copy the values
    for (uInt i=0; i < ac.nelements(); i++)
        glishComplexPtr[i] = complex(aipsComplexPtr[i].real(),
    				 aipsComplexPtr[i].imag());
    
    // Delete pointer, if necessary.
    ac.putStorage(aipsComplexPtr, del);
    				 
    // OK; create the Glish Value from the initialized storage
    Value native(ptr, ac.nelements());
    
    // Now we need to attach the shape to the Glish Value as an attribute
    IPosition acShape = ac.shape();
    int shapeArray[ac.ndim()];
    for (i=0; i < ac.ndim(); i++)
        shapeArray[i] = acShape(i);
    
    Value *shapeValuePtr = new Value(shapeArray, ac.ndim(), COPY_ARRAY);
    if (shapeValuePtr == 0) { ... memory error ...;}
    native.AssignAttribute("shape", shapeValuePtr);
    Unref(shapeValuePtr);
    // Done! native now contains a copy of ac.
    

To Do

• Delete attributes
• Get all attribute names
• Due to the way that Glish initializes itself, GlishValue isn't entirely reliable unless a GlishSysEvent source object also exists (e.g. false_value won't be defined). Since it isn't likely that one would want to use GlishValues without an event source this isn't too onerous, it should still be fixed (requires Glish client library changes). Getting the Glish reporters initialized is the other known problem.

Member Description

enum ValueType

A scalar is just a length=1 array in Glish.

GlishValue()

GlishValue(Value *value, Bool copy=False)

This should *only* be used for clients written using the interface which want to take advantage of the AIPS++ wrappers. This references value.

GlishValue(const GlishValue &other)

Create a logical copy of other. The physical copy is avoided for as long as possible (copy-on-write semantics).

virtual ~GlishValue()

GlishValue &operator=(const GlishValue &other)

Create a logical copy of other. The physical copy is avoided for as long as possible (copy-on-write semantics).

void addAttribute(const String &name, const GlishValue &value)

Add an attribute (named GlishValue) to this Value. Note that attributes can in turn have attributes (although this might not be very useful). The only attribute that is systematically used by Glish presently (Oct 94) is a "shape" which is an integer array containing the axis lengths. It is automatically supplied however by the GlishArray class.

Bool attributeExists(const String &name) const

GlishValue getAttribute(const String &name) const

ValueType type() const

Is this object an array or a record?

uInt nelements() const

The number of elements in an array (1 for a scalar), or the number of fields in a record.

String format(uInt maxArrayLength=10) const

Returns a String representation of this GlishValue object. The iostream output operator is also defined. By default only print the first 10 elements of an array.

virtual Bool ok() const

Is this GlishValue consistent?

const Value *value() const

The following might be useful for interfacing to native Glish classes occasionally - however it was mostly put in to allow testing of whether copy-on-write was working.

Bool isUnset() const

Is the glish value the unset value?

static const GlishRecord& getUnset()

Get the unset value;

void copyset(const Value *value)

Bool isUnsetPriv() const

output GlishValue to an ostream (in ASCII) (source)

Interface

ostream &operator<<(ostream &os, const GlishValue &value)

Description

Member Description

ostream &operator<<(ostream &os, const GlishValue &value)