
/**
 * Part of the D programming language runtime library.
 * Forms the symbols available to all D programs. Includes
 * Object, which is the root of the class object hierarchy.
 *
 * This module is implicitly imported.
 * Macros:
 *	WIKI = Phobos/Object
 */

/*
 *  Copyright (C) 2004-2007 by Digital Mars, www.digitalmars.com
 *  Written by Walter Bright
 *
 *  This software is provided 'as-is', without any express or implied
 *  warranty. In no event will the authors be held liable for any damages
 *  arising from the use of this software.
 *
 *  Permission is granted to anyone to use this software for any purpose,
 *  including commercial applications, and to alter it and redistribute it
 *  freely, in both source and binary form, subject to the following
 *  restrictions:
 *
 *  o  The origin of this software must not be misrepresented; you must not
 *     claim that you wrote the original software. If you use this software
 *     in a product, an acknowledgment in the product documentation would be
 *     appreciated but is not required.
 *  o  Altered source versions must be plainly marked as such, and must not
 *     be misrepresented as being the original software.
 *  o  This notice may not be removed or altered from any source
 *     distribution.
 */


module object;

import std.outofmemory;

extern (C)
{   /// C's printf function.
    int printf(in char *, ...);

    int memcmp(in void *, in void *, size_t);
    void* memcpy(void *, in void *, size_t);
    void* calloc(size_t, size_t);
    void* realloc(void*, size_t);
    void free(void*);

    Object _d_newclass(ClassInfo ci);
}

/// Standard boolean type.
alias bool bit;

version (X86_64)
{
    /**
     * An unsigned integral type large enough to span the memory space. Use for
     * array indices and pointer offsets for maximal portability to
     * architectures that have different memory address ranges. This is
     * analogous to C's size_t.
     */
    alias ulong size_t;

    /**
     * A signed integral type large enough to span the memory space. Use for
     * pointer differences and for size_t differences for maximal portability to
     * architectures that have different memory address ranges. This is
     * analogous to C's ptrdiff_t.
     */
    alias long ptrdiff_t;

    alias ulong hash_t;
}
else
{
    alias uint size_t;
    alias int ptrdiff_t;
    alias uint hash_t;
}

alias const(char)[] string;
alias const(wchar)[] wstring;
alias const(dchar)[] dstring;

/* *************************
 * Internal struct pointed to by the hidden .monitor member.
 */
struct Monitor
{
    void delegate(Object)[] delegates;

    /* More stuff goes here defined by internal/monitor.c */
}

/******************
 * All D class objects inherit from Object.
 */
class Object
{
    void print()
    {
	printf("%.*s\n", toString());
    }

    /**
     * Convert Object to a human readable string.
     */
    string toString()
    {
	return this.classinfo.name;
    }

    /**
     * Compute hash function for Object.
     */
    hash_t toHash()
    {
	// BUG: this prevents a compacting GC from working, needs to be fixed
	return cast(uint)cast(void *)this;
    }

    /**
     * Compare with another Object obj.
     * Returns:
     *	$(TABLE
     *  $(TR $(TD this &lt; obj) $(TD &lt; 0))
     *  $(TR $(TD this == obj) $(TD 0))
     *  $(TR $(TD this &gt; obj) $(TD &gt; 0))
     *  )
     */
    int opCmp(Object o)
    {
	// BUG: this prevents a compacting GC from working, needs to be fixed
	//return cast(int)cast(void *)this - cast(int)cast(void *)o;

	throw new Error("need opCmp for class " ~ this.classinfo.name);
    }

    /**
     * Returns !=0 if this object does have the same contents as obj.
     */
    int opEquals(Object o)
    {
	return cast(int)(this is o);
    }

    /* **
     * Call delegate dg, passing this to it, when this object gets destroyed.
     * Use extreme caution, as the list of delegates is stored in a place
     * not known to the gc. Thus, if any objects pointed to by one of these
     * delegates gets freed by the gc, calling the delegate will cause a
     * crash.
     * This is only for use by library developers, as it will need to be
     * redone if weak pointers are added or a moving gc is developed.
     */
    final void notifyRegister(void delegate(Object) dg)
    {
	//printf("notifyRegister(dg = %llx, o = %p)\n", dg, this);
	synchronized (this)
	{
	    Monitor* m = cast(Monitor*)(cast(void**)this)[1];
	    foreach (inout x; m.delegates)
	    {
		if (!x || x == dg)
		{   x = dg;
		    return;
		}
	    }

	    // Increase size of delegates[]
	    auto len = m.delegates.length;
	    auto startlen = len;
	    if (len == 0)
	    {
		len = 4;
		auto p = calloc((void delegate(Object)).sizeof, len);
		if (!p)
		    _d_OutOfMemory();
		m.delegates = (cast(void delegate(Object)*)p)[0 .. len];
	    }
	    else
	    {
		len += len + 4;
		auto p = realloc(m.delegates.ptr, (void delegate(Object)).sizeof * len);
		if (!p)
		    _d_OutOfMemory();
		m.delegates = (cast(void delegate(Object)*)p)[0 .. len];
		m.delegates[startlen .. len] = null;
	    }
	    m.delegates[startlen] = dg;
	}
    }

    /* **
     * Remove delegate dg from the notify list.
     * This is only for use by library developers, as it will need to be
     * redone if weak pointers are added or a moving gc is developed.
     */
    final void notifyUnRegister(void delegate(Object) dg)
    {
	synchronized (this)
	{
	    Monitor* m = cast(Monitor*)(cast(void**)this)[1];
	    foreach (inout x; m.delegates)
	    {
		if (x == dg)
		    x = null;
	    }
	}
    }

    /******
     * Create instance of class specified by classname.
     * The class must either have no constructors or have
     * a default constructor.
     * Returns:
     *	null if failed
     */
    static Object factory(string classname)
    {
	auto ci = ClassInfo.find(classname);
	if (ci)
	{
	    return ci.create();
	}
	return null;
    }
}

extern (C) void _d_notify_release(Object o)
{
    //printf("_d_notify_release(o = %p)\n", o);
    Monitor* m = cast(Monitor*)(cast(void**)o)[1];
    if (m.delegates.length)
    {
	auto dgs = m.delegates;
	synchronized (o)
	{
	    dgs = m.delegates;
	    m.delegates = null;
	}

	foreach (dg; dgs)
	{
	    if (dg)
	    {	//printf("calling dg = %llx (%p)\n", dg, o);
		dg(o);
	    }
	}

	free(dgs.ptr);
    }
}


/**
 * Information about an interface.
 * A pointer to this appears as the first entry in the interface's vtbl[].
 */
struct Interface
{
    ClassInfo classinfo;	/// .classinfo for this interface (not for containing class)
    void *[] vtbl;
    int offset;			/// offset to Interface 'this' from Object 'this'
}

import std.moduleinit;
/**
 * Runtime type information about a class. Can be retrieved for any class type
 * or instance by using the .classinfo property.
 * A pointer to this appears as the first entry in the class's vtbl[].
 */
class ClassInfo : Object
{
    byte[] init;		/** class static initializer
				 * (init.length gives size in bytes of class)
				 */
    string name;		/// class name
    void *[] vtbl;		/// virtual function pointer table
    Interface[] interfaces;	/// interfaces this class implements
    ClassInfo base;		/// base class
    void *destructor;
    void (*classInvariant)(Object);
    uint flags;
    //	1:			// IUnknown
    //	2:			// has no possible pointers into GC memory
    //	4:			// has offTi[] member
    //	8:			// has constructors
    void *deallocator;
    OffsetTypeInfo[] offTi;
    void function(Object) defaultConstructor;	// default Constructor

    /*************
     * Search all modules for ClassInfo corresponding to classname.
     * Returns: null if not found
     */
    static ClassInfo find(string classname)
    {
	foreach (m; ModuleInfo.modules())
	{
	    //writefln("module %s, %d", m.name, m.localClasses.length);
	    foreach (c; m.localClasses)
	    {
		//writefln("\tclass %s", c.name);
		if (c.name == classname)
		    return c;
	    }
	}
	return null;
    }

    /********************
     * Create instance of Object represented by 'this'.
     */
    Object create()
    {
	if (flags & 8 && !defaultConstructor)
	    return null;
	Object o = _d_newclass(this);
	if (flags & 8 && defaultConstructor)
	{
	    defaultConstructor(o);
	}
	return o;
    }
}

private import std.string;

/**
 * Array of pairs giving the offset and type information for each
 * member in an aggregate.
 */
struct OffsetTypeInfo
{
    size_t offset;	/// Offset of member from start of object
    TypeInfo ti;	/// TypeInfo for this member
}


/**
 * Runtime type information about a type.
 * Can be retrieved for any type using a
 * <a href="../expression.html#typeidexpression">TypeidExpression</a>.
 */
class TypeInfo
{
    hash_t toHash()
    {	hash_t hash;

	foreach (char c; this.toString())
	    hash = hash * 9 + c;
	return hash;
    }

    int opCmp(Object o)
    {
	if (this is o)
	    return 0;
	TypeInfo ti = cast(TypeInfo)o;
	if (ti is null)
	    return 1;
	return std.string.cmp(this.toString(), ti.toString());
    }

    int opEquals(Object o)
    {
	/* TypeInfo instances are singletons, but duplicates can exist
	 * across DLL's. Therefore, comparing for a name match is
	 * sufficient.
	 */
	if (this is o)
	    return 1;
	TypeInfo ti = cast(TypeInfo)o;
	return cast(int)(ti && this.toString() == ti.toString());
    }

    /// Returns a hash of the instance of a type.
    hash_t getHash(void *p) { return cast(uint)p; }

    /// Compares two instances for equality.
    int equals(void *p1, void *p2) { return cast(int)(p1 == p2); }

    /// Compares two instances for &lt;, ==, or &gt;.
    int compare(void *p1, void *p2) { return 0; }

    /// Returns size of the type.
    size_t tsize() { return 0; }

    /// Swaps two instances of the type.
    void swap(void *p1, void *p2)
    {
	size_t n = tsize();
	for (size_t i = 0; i < n; i++)
	{   byte t;

	    t = (cast(byte *)p1)[i];
	    (cast(byte *)p1)[i] = (cast(byte *)p2)[i];
	    (cast(byte *)p2)[i] = t;
	}
    }

    /// Get TypeInfo for 'next' type, as defined by what kind of type this is,
    /// null if none.
    TypeInfo next() { return null; }

    /// Return default initializer, null if default initialize to 0
    void[] init() { return null; }

    /// Get flags for type: 1 means GC should scan for pointers
    uint flags() { return 0; }

    /// Get type information on the contents of the type; null if not available
    OffsetTypeInfo[] offTi() { return null; }
}

class TypeInfo_Typedef : TypeInfo
{
    string toString() { return name; }

    int opEquals(Object o)
    {   TypeInfo_Typedef c;

	return cast(int)
		(this is o ||
		((c = cast(TypeInfo_Typedef)o) !is null &&
		 this.name == c.name &&
		 this.base == c.base));
    }

    hash_t getHash(void *p) { return base.getHash(p); }
    int equals(void *p1, void *p2) { return base.equals(p1, p2); }
    int compare(void *p1, void *p2) { return base.compare(p1, p2); }
    size_t tsize() { return base.tsize(); }
    void swap(void *p1, void *p2) { return base.swap(p1, p2); }

    TypeInfo next() { return base.next(); }
    uint flags() { return base.flags(); }
    void[] init() { return m_init.length ? m_init : base.init(); }

    TypeInfo base;
    string name;
    void[] m_init;
}

class TypeInfo_Enum : TypeInfo_Typedef
{
}

class TypeInfo_Pointer : TypeInfo
{
    string toString() { return m_next.toString() ~ "*"; }

    int opEquals(Object o)
    {   TypeInfo_Pointer c;

	return this is o ||
		((c = cast(TypeInfo_Pointer)o) !is null &&
		 this.m_next == c.m_next);
    }

    hash_t getHash(void *p)
    {
        return cast(uint)*cast(void* *)p;
    }

    int equals(void *p1, void *p2)
    {
        return cast(int)(*cast(void* *)p1 == *cast(void* *)p2);
    }

    int compare(void *p1, void *p2)
    {
	if (*cast(void* *)p1 < *cast(void* *)p2)
	    return -1;
	else if (*cast(void* *)p1 > *cast(void* *)p2)
	    return 1;
	else
	    return 0;
    }

    size_t tsize()
    {
	return (void*).sizeof;
    }

    void swap(void *p1, void *p2)
    {	void* tmp;
	tmp = *cast(void**)p1;
	*cast(void**)p1 = *cast(void**)p2;
	*cast(void**)p2 = tmp;
    }

    TypeInfo next() { return m_next; }
    uint flags() { return 1; }

    TypeInfo m_next;
}

class TypeInfo_Array : TypeInfo
{
    string toString() { return value.toString() ~ "[]"; }

    int opEquals(Object o)
    {   TypeInfo_Array c;

	return cast(int)
	       (this is o ||
		((c = cast(TypeInfo_Array)o) !is null &&
		 this.value == c.value));
    }

    hash_t getHash(void *p)
    {	size_t sz = value.tsize();
	hash_t hash = 0;
	void[] a = *cast(void[]*)p;
	for (size_t i = 0; i < a.length; i++)
	    hash += value.getHash(a.ptr + i * sz);
        return hash;
    }

    int equals(void *p1, void *p2)
    {
	void[] a1 = *cast(void[]*)p1;
	void[] a2 = *cast(void[]*)p2;
	if (a1.length != a2.length)
	    return 0;
	size_t sz = value.tsize();
	for (size_t i = 0; i < a1.length; i++)
	{
	    if (!value.equals(a1.ptr + i * sz, a2.ptr + i * sz))
		return 0;
	}
        return 1;
    }

    int compare(void *p1, void *p2)
    {
	void[] a1 = *cast(void[]*)p1;
	void[] a2 = *cast(void[]*)p2;
	size_t sz = value.tsize();
	size_t len = a1.length;

        if (a2.length < len)
            len = a2.length;
        for (size_t u = 0; u < len; u++)
        {
            int result = value.compare(a1.ptr + u * sz, a2.ptr + u * sz);
            if (result)
                return result;
        }
        return cast(int)a1.length - cast(int)a2.length;
    }

    size_t tsize()
    {
	return (void[]).sizeof;
    }

    void swap(void *p1, void *p2)
    {	void[] tmp;
	tmp = *cast(void[]*)p1;
	*cast(void[]*)p1 = *cast(void[]*)p2;
	*cast(void[]*)p2 = tmp;
    }

    TypeInfo value;

    TypeInfo next()
    {
	return value;
    }

    uint flags() { return 1; }
}

class TypeInfo_StaticArray : TypeInfo
{
    string toString()
    {
	return value.toString() ~ "[" ~ std.string.toString(len) ~ "]";
    }

    int opEquals(Object o)
    {   TypeInfo_StaticArray c;

	return cast(int)
	       (this is o ||
		((c = cast(TypeInfo_StaticArray)o) !is null &&
		 this.len == c.len &&
		 this.value == c.value));
    }

    hash_t getHash(void *p)
    {	size_t sz = value.tsize();
	hash_t hash = 0;
	for (size_t i = 0; i < len; i++)
	    hash += value.getHash(p + i * sz);
        return hash;
    }

    int equals(void *p1, void *p2)
    {
	size_t sz = value.tsize();

        for (size_t u = 0; u < len; u++)
        {
	    if (!value.equals(p1 + u * sz, p2 + u * sz))
		return 0;
        }
        return 1;
    }

    int compare(void *p1, void *p2)
    {
	size_t sz = value.tsize();

        for (size_t u = 0; u < len; u++)
        {
            int result = value.compare(p1 + u * sz, p2 + u * sz);
            if (result)
                return result;
        }
        return 0;
    }

    size_t tsize()
    {
	return len * value.tsize();
    }

    void swap(void *p1, void *p2)
    {	void* tmp;
	size_t sz = value.tsize();
	ubyte[16] buffer;
	void* pbuffer;

	if (sz < buffer.sizeof)
	    tmp = buffer.ptr;
	else
	    tmp = pbuffer = (new void[sz]).ptr;

	for (size_t u = 0; u < len; u += sz)
	{   size_t o = u * sz;
	    memcpy(tmp, p1 + o, sz);
	    memcpy(p1 + o, p2 + o, sz);
	    memcpy(p2 + o, tmp, sz);
	}
	if (pbuffer)
	    delete pbuffer;
    }

    void[] init() { return value.init(); }
    TypeInfo next() { return value; }
    uint flags() { return value.flags(); }

    TypeInfo value;
    size_t len;
}

class TypeInfo_AssociativeArray : TypeInfo
{
    string toString()
    {
	return value.toString() ~ "[" ~ key.toString() ~ "]";
    }

    int opEquals(Object o)
    {   TypeInfo_AssociativeArray c;

	return this is o ||
		((c = cast(TypeInfo_AssociativeArray)o) !is null &&
		 this.key == c.key &&
		 this.value == c.value);
    }

    // BUG: need to add the rest of the functions

    size_t tsize()
    {
	return (char[int]).sizeof;
    }

    TypeInfo next() { return value; }
    uint flags() { return 1; }

    TypeInfo value;
    TypeInfo key;
}

class TypeInfo_Function : TypeInfo
{
    string toString()
    {
	return next.toString() ~ "()";
    }

    int opEquals(Object o)
    {   TypeInfo_Function c;

	return this is o ||
		((c = cast(TypeInfo_Function)o) !is null &&
		 this.next == c.next);
    }

    // BUG: need to add the rest of the functions

    size_t tsize()
    {
	return 0;	// no size for functions
    }

    TypeInfo next;
}

class TypeInfo_Delegate : TypeInfo
{
    string toString()
    {
	return next.toString() ~ " delegate()";
    }

    int opEquals(Object o)
    {   TypeInfo_Delegate c;

	return this is o ||
		((c = cast(TypeInfo_Delegate)o) !is null &&
		 this.next == c.next);
    }

    // BUG: need to add the rest of the functions

    size_t tsize()
    {	alias int delegate() dg;
	return dg.sizeof;
    }

    uint flags() { return 1; }

    TypeInfo next;
}

class TypeInfo_Class : TypeInfo
{
    string toString() { return info.name; }

    int opEquals(Object o)
    {   TypeInfo_Class c;

	return this is o ||
		((c = cast(TypeInfo_Class)o) !is null &&
		 this.info.name == c.classinfo.name);
    }

    hash_t getHash(void *p)
    {
	Object o = *cast(Object*)p;
	assert(o);
	return o.toHash();
    }

    int equals(void *p1, void *p2)
    {
	Object o1 = *cast(Object*)p1;
	Object o2 = *cast(Object*)p2;

	return (o1 is o2) || (o1 && o1.opEquals(o2));
    }

    int compare(void *p1, void *p2)
    {
	Object o1 = *cast(Object*)p1;
	Object o2 = *cast(Object*)p2;
	int c = 0;

	// Regard null references as always being "less than"
	if (o1 !is o2)
	{
	    if (o1)
	    {	if (!o2)
		    c = 1;
		else
		    c = o1.opCmp(o2);
	    }
	    else
		c = -1;
	}
	return c;
    }

    size_t tsize()
    {
	return Object.sizeof;
    }

    uint flags() { return 1; }

    OffsetTypeInfo[] offTi()
    {
	return (info.flags & 4) ? info.offTi : null;
    }

    ClassInfo info;
}

class TypeInfo_Interface : TypeInfo
{
    string toString() { return info.name; }

    int opEquals(Object o)
    {   TypeInfo_Interface c;

	return this is o ||
		((c = cast(TypeInfo_Interface)o) !is null &&
		 this.info.name == c.classinfo.name);
    }

    hash_t getHash(void *p)
    {
	Interface* pi = **cast(Interface ***)*cast(void**)p;
	Object o = cast(Object)(*cast(void**)p - pi.offset);
	assert(o);
	return o.toHash();
    }

    int equals(void *p1, void *p2)
    {
	Interface* pi = **cast(Interface ***)*cast(void**)p1;
	Object o1 = cast(Object)(*cast(void**)p1 - pi.offset);
	pi = **cast(Interface ***)*cast(void**)p2;
	Object o2 = cast(Object)(*cast(void**)p2 - pi.offset);

	return o1 == o2 || (o1 && o1.opCmp(o2) == 0);
    }

    int compare(void *p1, void *p2)
    {
	Interface* pi = **cast(Interface ***)*cast(void**)p1;
	Object o1 = cast(Object)(*cast(void**)p1 - pi.offset);
	pi = **cast(Interface ***)*cast(void**)p2;
	Object o2 = cast(Object)(*cast(void**)p2 - pi.offset);
	int c = 0;

	// Regard null references as always being "less than"
	if (o1 != o2)
	{
	    if (o1)
	    {	if (!o2)
		    c = 1;
		else
		    c = o1.opCmp(o2);
	    }
	    else
		c = -1;
	}
	return c;
    }

    size_t tsize()
    {
	return Object.sizeof;
    }

    uint flags() { return 1; }

    ClassInfo info;
}

class TypeInfo_Struct : TypeInfo
{
    string toString() { return name; }

    int opEquals(Object o)
    {   TypeInfo_Struct s;

	return this is o ||
		((s = cast(TypeInfo_Struct)o) !is null &&
		 this.name == s.name &&
		 this.init.length == s.init.length);
    }

    hash_t getHash(void *p)
    {	hash_t h;

	assert(p);
	if (xtoHash)
	{   //printf("getHash() using xtoHash\n");
	    h = (*xtoHash)(p);
	}
	else
	{
	    //printf("getHash() using default hash\n");
	    // A sorry hash algorithm.
	    // Should use the one for strings.
	    // BUG: relies on the GC not moving objects
	    for (size_t i = 0; i < init.length; i++)
	    {	h = h * 9 + *cast(ubyte*)p;
		p++;
	    }
	}
	return h;
    }

    int equals(void *p2, void *p1)
    {	int c;

	if (p1 == p2)
	    c = 1;
	else if (!p1 || !p2)
	    c = 0;
	else if (xopEquals)
	    c = (*xopEquals)(p1, p2);
	else
	    // BUG: relies on the GC not moving objects
	    c = (memcmp(p1, p2, init.length) == 0);
	return c;
    }

    int compare(void *p2, void *p1)
    {
	int c = 0;

	// Regard null references as always being "less than"
	if (p1 != p2)
	{
	    if (p1)
	    {	if (!p2)
		    c = 1;
		else if (xopCmp)
		    c = (*xopCmp)(p1, p2);
		else
		    // BUG: relies on the GC not moving objects
		    c = memcmp(p1, p2, init.length);
	    }
	    else
		c = -1;
	}
	return c;
    }

    size_t tsize()
    {
	return init.length;
    }

    void[] init() { return m_init; }

    uint flags() { return m_flags; }

    string name;
    void[] m_init;	// initializer; init.ptr == null if 0 initialize

    hash_t function(void*) xtoHash;
    int function(void*,void*) xopEquals;
    int function(void*,void*) xopCmp;
    string function(void*) xtoString;

    uint m_flags;
}

class TypeInfo_Tuple : TypeInfo
{
    TypeInfo[] elements;

    string toString()
    {
	string s;
	s = "(";
	foreach (i, element; elements)
	{
	    if (i)
		s ~= ',';
	    s ~= element.toString();
	}
	s ~= ")";
        return s;
    }

    int opEquals(Object o)
    {
	if (this is o)
	    return 1;

	auto t = cast(TypeInfo_Tuple)o;
	if (t && elements.length == t.elements.length)
	{
	    for (size_t i = 0; i < elements.length; i++)
	    {
		if (elements[i] != t.elements[i])
		    return 0;
	    }
	    return 1;
	}
	return 0;
    }

    hash_t getHash(void *p)
    {
        assert(0);
    }

    int equals(void *p1, void *p2)
    {
        assert(0);
    }

    int compare(void *p1, void *p2)
    {
        assert(0);
    }

    size_t tsize()
    {
        assert(0);
    }

    void swap(void *p1, void *p2)
    {
        assert(0);
    }
}

class TypeInfo_Const : TypeInfo
{
    string toString() { return "const " ~ base.toString(); }

    int opEquals(Object o) { return base.opEquals(o); }
    hash_t getHash(void *p) { return base.getHash(p); }
    int equals(void *p1, void *p2) { return base.equals(p1, p2); }
    int compare(void *p1, void *p2) { return base.compare(p1, p2); }
    size_t tsize() { return base.tsize(); }
    void swap(void *p1, void *p2) { return base.swap(p1, p2); }

    TypeInfo next() { return base.next(); }
    uint flags() { return base.flags(); }
    void[] init() { return base.init(); }

    TypeInfo base;
}

class TypeInfo_Invariant : TypeInfo_Const
{
    string toString() { return "invariant " ~ base.toString(); }
}


/**
 * All recoverable exceptions should be derived from class Exception.
 */
class Exception : Object
{
    string msg;

    /**
     * Constructor; msg is a descriptive message for the exception.
     */
    this(string msg)
    {
	this.msg = msg;
    }

    void print()
    {
	printf("%.*s\n", toString());
    }

    string toString() { return msg; }
}

/**
 * All irrecoverable exceptions should be derived from class Error.
 */
class Error : Exception
{
    Error next;

    /**
     * Constructor; msg is a descriptive message for the exception.
     */
    this(string msg)
    {
	super(msg);
    }

    this(string msg, Error next)
    {
	super(msg);
	this.next = next;
    }
}

//extern (C) int nullext = 0;

