| Description |
A new HashTable is created with the same number of elements, attributes and key-value entries as the current HashTable.
When the current table holds reference (non primitive) data types, the cloned table element values still refer to the same objects that current table elements refer to. This is what is referred to as a shallow copy. A deep copy would create new versions of the referred objects.
|
| | Notes | You are obliged to cast the resultant Object to a HashTable before assignment to a HashTable variable.
|
|
| Microsoft MSDN Links |
System.Collections
System.Collections.HashTable
|
|
|
| A simple example |
program Project1;
{$APPTYPE CONSOLE}
uses
System.Collections;
var
Source, Target : System.Collections.HashTable;
DictEntry : DictionaryEntry;
Enumerator : IEnumerator;
begin
// Create our hash tables
Source := HashTable.Create;
Target := HashTable.Create;
// Add entries to the Source table
Source['Name'] := 'Neil Moffatt';
Source['Age'] := TObject(47);
Source['Birthday'] := DateTime.Create(1957, 2, 18);
// Display the Source table
Console.WriteLine('Source table :');
Console.WriteLine;
Enumerator := Source.GetEnumerator;
while Enumerator.MoveNext do
begin
DictEntry := DictionaryEntry(Enumerator.Current);
Console.WriteLine('{0} = {1}',
DictEntry.Key.ToString,
DictEntry.Value.ToString);
end;
// Clone the Source table to the Target table
Target := HashTable(Source.Clone);
// Display the Target table
Console.WriteLine;
Console.WriteLine('Target table :');
Console.WriteLine;
Enumerator := Source.GetEnumerator;
while Enumerator.MoveNext do
begin
DictEntry := DictionaryEntry(Enumerator.Current);
Console.WriteLine('{0} = {1}',
DictEntry.Key.ToString,
DictEntry.Value.ToString);
end;
Console.Readline;
end.
| | Show full unit code | Source table :
Birthday = 18/02/1957 00:00:00
Age = 47
Name = Neil Moffatt
Target table :
Birthday = 18/02/1957 00:00:00
Age = 47
Name = Neil Moffatt
| | | Illustrating the shallowness of the Clone method | program Project1;
{$APPTYPE CONSOLE}
uses
System.Collections;
var
Source, Target : System.Collections.HashTable;
DictEntry : DictionaryEntry;
Enumerator : IEnumerator;
begin
// Create our hash tables
Source := HashTable.Create;
Target := HashTable.Create;
// Add entries to the Source table
Source['Name'] := 'Neil Moffatt';
Source['Age'] := TObject(47);
Source['Birthday'] := DateTime.Create(1957, 2, 18);
// Display the Source table
Console.WriteLine('Source table :');
Console.WriteLine;
Enumerator := Source.GetEnumerator;
while Enumerator.MoveNext do
begin
// Note that entries are returned in key sorted order
DictEntry := DictionaryEntry(Enumerator.Current);
Console.WriteLine('{0} = {1}',
DictEntry.Key.ToString,
DictEntry.Value.ToString);
end;
// Clone the Source table to the Target table
Target := HashTable(Source.Clone);
// Display the Target table
Console.WriteLine;
Console.WriteLine('Target table :');
Console.WriteLine;
Enumerator := Source.GetEnumerator;
while Enumerator.MoveNext do
begin
// Note that entries are returned in key sorted order
DictEntry := DictionaryEntry(Enumerator.Current);
Console.WriteLine('{0} = {1}',
DictEntry.Key.ToString,
DictEntry.Value.ToString);
end;
// Update the birthday value in just the Source
Console.WriteLine;
Console.WriteLine('Updating just the Source Birthday :');
Console.WriteLine;
Source['Birthday'] := DAteTime.Create(2000,1,1);
// Display the Source table
Console.WriteLine('Source table :');
Console.WriteLine;
Enumerator := Source.GetEnumerator;
while Enumerator.MoveNext do
begin
// Note that entries are returned in key sorted order
DictEntry := DictionaryEntry(Enumerator.Current);
Console.WriteLine('{0} = {1}',
DictEntry.Key.ToString,
DictEntry.Value.ToString);
end;
// Display the Target table
Console.WriteLine;
Console.WriteLine('Target table :');
Console.WriteLine;
Enumerator := Source.GetEnumerator;
while Enumerator.MoveNext do
begin
// Note that entries are returned in key sorted order
DictEntry := DictionaryEntry(Enumerator.Current);
Console.WriteLine('{0} = {1}',
DictEntry.Key.ToString,
DictEntry.Value.ToString);
end;
Console.Readline;
end.
| | Show full unit code | Source table :
Birthday = 18/02/1957 00:00:00
Age = 47
Name = Neil Moffatt
Target table :
Birthday = 18/02/1957 00:00:00
Age = 47
Name = Neil Moffatt
Updating just the Source Birthday :
Source table :
Birthday = 01/01/2000 00:00:00
Age = 47
Name = Neil Moffatt
Target table :
Birthday = 01/01/2000 00:00:00
Age = 47
Name = Neil Moffatt
|
| |
|
|
|