lazarus/docs/xml/lazutils/stringhashlist.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--

Documentation for LCL (Lazarus Component Library) and LazUtils (Lazarus 
Utilities) are published under the Creative Commons Attribution-ShareAlike 4.0 
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Copyright (c) 1997-2025, by the Lazarus Development Team.

-->
<fpdoc-descriptions>
<package name="lazutils">
<!--
====================================================================
StringHashList
====================================================================
-->
<module name="StringHashList">
<short>Implements a hashed list of string values.</short>
<descr>
<p>
<file>stringhashlist.pas</file> contains types, classes, and routines used to 
implement a hashed list of string values.
</p>
<p>
<file>stringhashlist.pas</file> is part of the <file>lazutils</file> package.
</p>
<p>
Thanks to Markus Waldenburg.
</p>
</descr>

<!-- unresolved external references -->
<element name="Classes"/>
<element name="SysUtils"/>
<element name="LazUtilsStrConsts"/>

<element name="PStringHashItem">
<short>Pointer to a TStringHashItem instance.</short>
</element>

<element name="TStringHashItem">
<short>Record type used to represent a hash item for a String value.</short>
<descr>
<p>
<var>TStringHashItem</var> is a <b>record</b> type which represents a hash 
item for a String value. It has members for the Cardinal hash value, the 
String for the hash value, and a pointer to Data associated with the hash 
item.
</p>
<p>
TStringHashItem pointers are the type added to the TStringHashList container.
</p>
</descr>
<seealso>
<link id="PStringHashItem"/>
<link id="TStringHashList"/>
</seealso>
</element>

<element name="TStringHashItem.HashValue">
<short>Cardinal hash value for the characters in Key.</short>
</element>

<!-- variable Visibility: default -->
<element name="TStringHashItem.Key">
<short>String with the content used to generate the HashValue.</short>
</element>

<element name="TStringHashItem.Data">
<short>
Untyped Pointer to arbitrary data associated with the Key and HashValue.
</short>
</element>

<element name="PStringHashItemList">
<short>Pointer to a block of TStringHashItem instances.</short>
<descr>
<p>
Implements the storage used in the <var>TStringHashList</var> class.
</p>
</descr>
<seealso>
<link id="TStringHashItem"/>
<link id="TStringHashList"/>
</seealso>
</element>

<element name="TStringHashList">
<short>
Implements a container used to store hashed item values, keys, and data.
</short>
<descr>
<p>
<var>TStringHashList</var> is a <var>TObject</var> descendant which 
implements a container for hash values, keys, and data for <var>String</var> 
types.
</p>
<p>
TStringHashList uses the PStringHashItem type to represent the items stored 
in the container. This provides a 32-bit hash value, which can reflect the 
case for the String value if desired. It also includes an untyped pointer to 
arbitrary data associated with the hashed item (when provided). Items in the 
container are stored in hash value order, and uses a binary search for 
retrieval.
</p>
<p>
Use the Add method to add String values, and optional pointers to their data, 
to the container.
</p>
<p>
Use the Find method to get the position of an item in the container using its 
String value.
</p>
<p>
Use the Remove method to delete a hash item with the specified String value.
</p>
<p>
Use the Clear method to remove all hashed items in the container.
</p>
<p>
Use the Count property to determine the number of hashed items stored in the 
container.
</p>
<p>
Use the List property to access the storage for the container. It can be used 
for indexed access to the PStringHashItemList pointers with the hash value, 
key, and data for the items.
</p>
<p>
Use the Data property to get an untyped pointer to the arbitrary data 
associated with the hash item with a given key (String). The pointer must be 
cast to the type needed in the application.
</p>
<p>
Use the CaseSensitive property to control whether the case for a Key value is 
used when the hash value is generated, or retrieved in the Find method. When 
set to <b>False</b>, the key value is converted to its uppercase equivalent 
when the hash value is generated or retrieved. The value in CaseSensitive 
must be assigned before any hash items are added to the container; an 
exception is raised when the property value is changed and the container is 
not empty.
</p>
</descr>
<seealso>
</seealso>
</element>

<element name="TStringHashList.FList"/>
<element name="TStringHashList.FCount"/>
<element name="TStringHashList.FCaseSensitive"/>

<element name="TStringHashList.BinarySearch"/>
<element name="TStringHashList.BinarySearch.Result"/>
<element name="TStringHashList.BinarySearch.HashValue"/>

<element name="TStringHashList.CompareString"/>
<element name="TStringHashList.CompareString.Result"/>
<element name="TStringHashList.CompareString.Value1"/>
<element name="TStringHashList.CompareString.Value2"/>

<element name="TStringHashList.CompareValue"/>
<element name="TStringHashList.CompareValue.Result"/>
<element name="TStringHashList.CompareValue.Value1"/>
<element name="TStringHashList.CompareValue.Value2"/>

<element name="TStringHashList.FindHashBoundaries"/>
<element name="TStringHashList.FindHashBoundaries.HashValue"/>
<element name="TStringHashList.FindHashBoundaries.StartFrom"/>
<element name="TStringHashList.FindHashBoundaries.First"/>
<element name="TStringHashList.FindHashBoundaries.Last"/>

<element name="TStringHashList.GetData"/>
<element name="TStringHashList.GetData.Result"/>
<element name="TStringHashList.GetData.S"/>

<element name="TStringHashList.SetCaseSensitive"/>
<element name="TStringHashList.SetCaseSensitive.Value"/>

<element name="TStringHashList.Delete"/>
<element name="TStringHashList.Delete.Index"/>

<element name="TStringHashList.SetData"/>
<element name="TStringHashList.SetData.S"/>
<element name="TStringHashList.SetData.AValue"/>

<element name="TStringHashList.HashOf">
<short>Calculates the hash value for the specified String.</short>
<descr>
<p>
<var>HashOf</var> is a <var>Cardinal</var> function used to calculate and 
return the 32-bit hash value for the String in Key. HashOf examines all bytes 
values in Key (in reverse order). When CaseSensitive is set to <b>False</b>, 
the characters are converted to their uppercase equivalent for use in the 
hashing algorithm. Range and overflow checking are disabled in the HashOf 
method.
</p>
<p>
HashOf is used in the Add method to calculate the HashValue stored in the 
PStringHashItem entry for the hash item. It is also used in the Find method 
to get the hash value to locate in the storage for the List.
</p>
</descr>
<seealso>
<link id="TStringHashList.Add"/>
<link id="TStringHashList.Find"/>
<link id="TStringHashList.CaseSensitive"/>
<link id="TStringHashList.List"/>
<link id="PStringHashItem"/>
</seealso>
</element>
<element name="TStringHashList.HashOf.Result">
<short>Cardinal hash value for the specified Key.</short>
</element>
<element name="TStringHashList.HashOf.Key">
<short>
String used to calculate the hash value for an item in the list.
</short>
</element>

<element name="TStringHashList.Insert">
<short>Stores a hash item at the specified position in the container.</short>
<descr>
<p>
<var>Insert</var> is a method used to store the pointer in Item to the 
internal storage in List. Insert re-allocates the memory used for List to 
include the addition space needed for the new item.
</p>
<p>
Index contains the ordinal position in List where the PStringHashItem 
instance is stored. Index must be in the range 0..Count. When Index has the 
value in Count, Insert behaves like an Append operation in the List. The 
value Index is adjusted if it exceeds either range limit.
</p>
<p>
When Index is not the newly added position (Count), the memory for existing 
entries in List are shifted upward by the size of the hash item in Item. The 
pointer in Item is stored in List at the ordinal position in Index.
</p>
<p>
Inserts increments the value in the Count property for the newly added item 
in the container.
</p>
<p>
Insert is used to implement the Add method.
</p>
</descr>
<seealso>
</seealso>
</element>
<element name="TStringHashList.Insert.Index">
<short>Ordinal position in List for the specified hash item.</short>
</element>
<element name="TStringHashList.Insert.Item">
<short>Hash item inserted in the method.</short>
</element>

<element name="TStringHashList.Create">
<short>Constructor for the class instance.</short>
<descr>
<p>
<var>Create</var> is the constructor for the class instance. It sets the 
value in the CaseSensitive property to the value specified in the 
CaseSensitivity argument. Create calls the inherited (empty) constructor 
prior to exiting from the method.
</p>
</descr>
<seealso>
<link id="TStringHashList.CaseSensitive"/>
</seealso>
</element>
<element name="TStringHashList.Create.CaseSensitivity">
<short>
Default value for the CaseSensitive property in the class instance.
</short>
</element>

<element name="TStringHashList.Destroy">
<short>Destructor for the class instance.</short>
<descr>
<p>
<var>Destroy</var> is the overridden destructor for the class instance. It 
calls the Clear method to remove free any hash items and the storage 
allocated in List. Destroy calls the inherited method prior to exit.
</p>
</descr>
<seealso>
<link id="TStringHashList.Clear"/>
<link id="TStringHashList.List"/>
</seealso>
</element>

<element name="TStringHashList.Add">
<short>Adds a hash item and optional data to the container.</short>
<descr>
<p>
<var>Add</var> is an overloaded Integer function used to store a hash item 
(and optional data associated with item) in the List for the container. The 
return value contains the ordinal position in List where the hash item was 
stored.
</p>
<p>
S is a String with the key used to construct the hash value.
</p>
<p>
ItemData is an untyped pointer to the optional data associated with the key.
</p>
<p>
Add allocates a new PStringHashItem instance used to represent the hash item 
in ItemData. Values in S and itemData are stored in the instance. HashOf is 
called to get the 32-bit hash value stored in the instance.
</p>
<p>
Hash items in List are stored in hash value order. When Count has a non-zero 
value, the hash value for the new entry is used to locate the position in 
List where the new entry is stored. When Count is 0, the item is always 
stored at position 0 in List.
</p>
<p>
Use Remove to delete a hash item in List with a given key value.
</p>
<p>
Use Find to get the position in List for a hash item with a given key value.
</p>
<p>
Use the Data property to get an untyped pointer to the arbitrary data 
associated with the given key value. The pointer must be cast to the type 
needed in the application.
</p>
<p>
Use List to access the PStringHashItemList using an ordinal position in the 
storage.
</p>
</descr>
<seealso>
</seealso>
</element>
<element name="TStringHashList.Add.Result">
<short>Ordinal position in List where the new hash item was stored.</short>
</element>
<element name="TStringHashList.Add.S">
<short>Key value for the hash item.</short>
</element>
<element name="TStringHashList.Add.ItemData">
<short>Untyped pointer to the optional data for the specified key.</short>
</element>

<element name="TStringHashList.Clear">
<short>
Frees resources allocated for hash items and the storage for the list.
</short>
<descr>
<p>
<var>Clear</var> is a method used to free resources allocated for the hash 
items, and the memory allocated for the List property.
</p>
<p>
Clear calls Dispose for each of the PStringHashItem instances stored in List 
to free the memory allocated for the typed pointer. Clear calls FreeMem to 
free the memory allocated for the List property, and sets the member 
reference to Nil.
</p>
<p>
The value in Count is set to 0 to indicate that the List is empty.
</p>
<p>
Clear is called from the Destroy method when the class instance is freed.
</p>
</descr>
<seealso>
<link id="TStringHashList.List"/>
<link id="TStringHashList.Count"/>
<link id="TStringHashList.Destroy"/>
<link id="PStringHashItemList"/>
<link id="PStringHashItem"/>
</seealso>
</element>

<element name="TStringHashList.Find">
<short>
Gets the ordinal position in List where the specified key (and data) are 
stored.
</short>
<descr>
<p>
<var>Find</var> is an Integer function used to the position in List where the 
hash item with the specified Key value is stored. The return value contains 
the ordinal position for the hash item in List, or -1 when a hash item is not 
found for the key value in S.
</p>
<p>
S contains the key value for the hash item locates in the method. HashOf is 
called to get the 32-bit hash value, and BinarySearch is called to locate the 
hash value in List.
</p>
<p>
An overloaded variant provides an untyped pointer in Data that is also used 
to locate the hash item. If the value in Data does not match the stored value 
in List, other candidates with the same hash value are considered. A match is 
found when the Key and Data for the hash item are the same. Otherwise, the 
return value is set to -1 to indicate that a match was not found.
</p>
<p>
Find is used in the Remove method, and to implement indexed access for the 
Data property.
</p>
</descr>
<seealso>
</seealso>
</element>
<element name="TStringHashList.Find.Result">
<short>
Ordinal position for the requested hash item, or -1 when not found.
</short>
</element>
<element name="TStringHashList.Find.S">
<short>Key value for the hash item to locate in the List.</short>
</element>
<element name="TStringHashList.Find.Data">
<short>Untyped pointer to the optional data for the hash item.</short>
</element>

<element name="TStringHashList.Remove">
<short>
Frees resources allocated for the hash item and deletes it from the List.
</short>
<descr>
<p>
<var>Remove</var> is a method used to remove a hash item in List with the 
specified key value (and optional data).
</p>
<p>
S contains the key value to locate in the List.
</p>
<p>
Data is an untyped Pointer to the optional data associated with the key value.
</p>
<p>
Remove calls the Find method to get the ordinal position in List where the 
hash item is stored, or -1 when a hash item with the key (and optional data) 
is not found. The position is used as the return value for the method.
</p>
<p>
When a hash item was located, the Dispose routine is called to free the 
memory allocated for the typed Pointer to the hash item. Delete is called to 
remove the PHashStringItem instance and re-order the memory for hash items 
after the position in List. The Count property is decremented to reflect the 
new size for the List.
</p>
</descr>
<seealso>
</seealso>
</element>
<element name="TStringHashList.Remove.Result">
<short>
Ordinal position in List for the removed hash item, or -1 when not found.
</short>
</element>
<element name="TStringHashList.Remove.S">
<short>Key value for the hash item removed in the method.</short>
</element>
<element name="TStringHashList.Remove.Data">
<short>Untyped pointer to the optional data for the hash item.</short>
</element>

<element name="TStringHashList.CaseSensitive">
<short>Indicates if case sensitivity is used for hash item keys.</short>
<descr>
<p>
<var>CaseSensitive</var> is a <var>Boolean</var> property which indicates the 
case for the key values in hash items. The default value for the property is 
set to the argument passed to the Create constructor.
</p>
<p>
When set to <b>False</b>, key values are converted to their uppercase 
equivalent when hash values are calculate in the HashOf method. When set to 
<b>True</b>, the existing case for the key value is used.
</p>
<p>
The value in CaseSensitive must be set before hash items are added to the 
List. Setting a new value for the property when Count has a non-zero value 
causes an EListError Exception to be raised.
</p>
<p>
CaseSensitive is used in the Find method to ensure that the search uses the 
same logic employed when the hash item was created.
</p>
</descr>
<seealso>
<link id="TStringHashList.HashOf"/>
<link id="TStringHashList.Find"/>
<link id="TStringHashList.Create"/>
<link id="#rtl.classes.EListError">EListError</link>
</seealso>
</element>

<element name="TStringHashList.Count">
<short>Number of hash items stored in the List property.</short>
<descr>
<p>
<var>Count</var> is a read-only <var>Integer</var> property which contains 
the number of hash items stored in List. The value is maintained when the 
Add, Insert, Remove, Delete, or Clear methods are called.
</p>
<p>
Count establishes the upper limit for indexed access to values in the List 
property; index values must be in the range 0..Count-1.
</p>
</descr>
<seealso>
</seealso>
</element>

<element name="TStringHashList.Data">
<short>
Provided indexed access to the data for a hash item using its key value.
</short>
<descr>
<p>
<var>Data</var> is an indexed <var>Pointer</var> property which provides 
access to the storage for a hash item by its key value. The untyped Pointer 
in the property values is arbitrary data associated with the key value, and 
must be cast to the type expected in an application.
</p>
<p>
The Find method is called when reading or writing a value in the property. 
Finds gets the position where the hash item is stored in List using the 
setting in the CaseSensitive property. If the value in S does not exist when 
reading a property value, Nil is returned. If the value in S does not exist 
when writing a property value, the Add method is called to create a new hash 
item in List with the key in S.
</p>
<p>
Data is the default property for the container, and the value used in an 
enumerator for the class instance.
</p>
</descr>
<seealso>
<link id="TStringHashList.List"/>
<link id="TStringHashList.Find"/>
<link id="TStringHashList.CaseSensitive"/>
<link id="TStringHashList.HashOf"/>
<link id="TStringHashList.Add"/>
</seealso>
</element>
<element name="TStringHashList.Data.S">
<short>Key value for the hash item.</short>
</element>

<element name="TStringHashList.List">
<short>Provides indexed access to the storage used in the container.</short>
<descr>
<p>
<var>List</var> is a read-only indexed <var>PStringHashItemList</var> 
property which provides access to the storage used in the container. 
Resources in List are allocated and freed in methods like Add, Remove, 
Delete, and Clear.
</p>
<p>
The value is a Pointer to the first memory block allocated for the 
PHashStringItem instances stored in the container. The property values are 
accessed using the ordinal position for a given hash item.
</p>
<p>
Since the property value is a Pointer, it must be dereferenced to access the 
member values for a given hash item. For example:
</p>
<code>
// var AKey: Cardinal;
// var AHashValue: String;
// var AData: TObject;
// var AHashes: TStringHashList;

AKey := AHashes.List[2]^.Key;
AHashValue := AHashes.List[2]^.HashValue;
AData := AHashes.List[2]^.Data;
</code>
</descr>
<seealso>
<link id="PStringHashItemList"/>
<link id="PStringHashItem"/>
</seealso>
</element>

</module>
<!-- StringHashList -->

</package>
</fpdoc-descriptions>