wyal.lang

Class WyalFile.Type.Null

java.lang.Object

wybs.lang.SyntacticElement.Impl

wybs.util.AbstractSyntacticItem

wyal.lang.WyalFile.Type.Atom

wyal.lang.WyalFile.Type.Null

All Implemented Interfaces:

Cloneable, Comparable<wybs.lang.SyntacticItem>, WyalFile.Type, WyalFile.Type.Primitive, wybs.lang.SyntacticElement, wybs.lang.SyntacticItem

Enclosing interface:

WyalFile.Type

public static class WyalFile.Type.Null
extends WyalFile.Type.Atom
implements WyalFile.Type.Primitive

The null type is a special type which should be used to show the absence of something. It is distinct from void, since variables can hold the special null value (where as there is no special "void" value). With all of the problems surrounding null and NullPointerExceptions in languages like Java and C, it may seem that this type should be avoided. However, it remains a very useful abstraction to have around and, in Whiley, it is treated in a completely safe manner (unlike e.g. Java).

Author:

David J. Pearce

Nested Class Summary

Nested classes/interfaces inherited from interface wyal.lang.WyalFile.Type

WyalFile.Type.Any, WyalFile.Type.Array, WyalFile.Type.Atom, WyalFile.Type.Bool, WyalFile.Type.Byte, WyalFile.Type.Function, WyalFile.Type.FunctionOrMacroOrInvariant, WyalFile.Type.FunctionOrMethodOrProperty, WyalFile.Type.Int, WyalFile.Type.Intersection, WyalFile.Type.Invariant, WyalFile.Type.Method, WyalFile.Type.Negation, WyalFile.Type.Nominal, WyalFile.Type.Null, WyalFile.Type.Primitive, WyalFile.Type.Property, WyalFile.Type.Record, WyalFile.Type.Reference, WyalFile.Type.Union, WyalFile.Type.UnionOrIntersection, WyalFile.Type.Void

Nested classes/interfaces inherited from interface wybs.lang.SyntacticItem

wybs.lang.SyntacticItem.Data, wybs.lang.SyntacticItem.Operands, wybs.lang.SyntacticItem.Schema

Nested classes/interfaces inherited from interface wybs.lang.SyntacticElement

wybs.lang.SyntacticElement.Impl

Field Summary

Fields inherited from class wybs.util.AbstractSyntacticItem

data, opcode, operands

Fields inherited from interface wyal.lang.WyalFile.Type

Any, Bool, Int, Null, Void

Constructor Summary

Constructors

Constructor and Description
Null()

Method Summary

Modifier and Type	Method and Description
WyalFile.Type.Null	clone(wybs.lang.SyntacticItem[] operands)
String	toString()

Methods inherited from class wybs.util.AbstractSyntacticItem

allocate, compareTo, equals, get, getAll, getAncestor, getData, getHeap, getIndex, getOpcode, getParent, hashCode, match, setOpcode, setOperand, size, toArray

Methods inherited from class wybs.lang.SyntacticElement.Impl

attribute, attributes

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface wybs.lang.SyntacticItem

allocate, get, getAll, getData, getHeap, getIndex, getOpcode, getParent, setOpcode, setOperand, size

Methods inherited from interface wybs.lang.SyntacticElement

attribute, attributes

Methods inherited from interface java.lang.Comparable

compareTo

Constructor Detail

Null

public Null()

Method Detail

clone

public WyalFile.Type.Null clone(wybs.lang.SyntacticItem[] operands)

Specified by:

clone in interface wybs.lang.SyntacticItem

toString

public String toString()

Overrides:

toString in class wybs.util.AbstractSyntacticItem