The table-extensions Module#
The Collections library’s table-extensions module extends the Dylan language’s standard table features.
Note
Open Dylan provides a slightly different table implementation from that described by the DRM. See Language Differences for details of these differences.
Basics#
The table-extensions module exports the classes <string-table> and
<case-insensitive-string-table>; the type <hash-state>; the
constructor macro table; the generic function remove-all-keys!
and two methods thereon; and the functions collection-hash,
sequence-hash, string-hash, values-hash,
case-insensitive-string-hash, and case-insensitive-equal.
The <string-table> class is a class of tables that use strings
for keys. <case-insensitive-string-table> is similar, but the keys
are considered to be case insensitive.
The <hash-state> type implements hash states. A hash state is
defined by the DRM, page 123, as “an implementation-dependent type that
is associated with a hash id and can be used by the implementation to
determine whether the hash id has been invalidated.” See pages 122–123
of the DRM for more details.
The various hash functions and the case-insensitive-equal
equivalence predicate are convenient building blocks for creating new
table classes and hash functions.
Hash functions#
Different hash functions are not required to return the same hash code for equal or even identical objects. For instance,
collection-hash(#(), object-hash, object-hash);
is not guaranteed to return the same values as
sequence-hash(#(), object-hash);
Furthermore, collection-hash with ordered: #t is not
guaranteed to return the same hash code as collection-hash with
ordered: #f. Such a requirement would render the ordered:
keyword useless.
Weak tables#
Open Dylan allows all general instances of the built-in class
<table> to be weak. See weak tables of
this volume for information about weakness.
You can create weak tables with the <table> class’s weak:
init-keyword. The legal values for this keyword are:
#"key"Creates a table with weak keys. When there are no longer any strong references to a key, the table entry of which it is part becomes eligible for garbage collection.#"value"Creates a table with weak values. When there are no longer any strong references to a value, the table entry of which it is a part becomes eligible for garbage collection.#fCreates a table with strong keys and values. This is the default value.
The table-extensions Module#
This section contains a reference description for each item exported from the module table-extensions.
- <string-table> Sealed Class#
A table class that uses strings for keys.
- Superclasses:
- Discussion:
The
<string-table>class is the class of tables that use instances of<string>for their keys. It is an error to use a key that is not an instance of<string>.Keys are compared with the equivalence predicate
\=.The elements of the table are instances of
<object>.Modifying the key once it has been used to add an element to a
<string-table>results in undefined behavior.
- <case-insensitive-string-table> Sealed Class#
A table class that uses case-insensitive strings for keys.
- Superclasses:
- Discussion:
The
<string-table>class is the class of tables that use instances of<string>for their keys. It is an error to use a key that is not an instance of<string>.Keys are compared with the equivalence predicate
case-insensitive-equal.The elements of the table are instances of
<object>.Modifying the key once it has been used to add an element to a
<case-insensitive-string-table>results in undefined behavior.
- <hash-state> Class#
A hash state.
- Superclasses:
- Discussion:
Anything that the Dylan Reference Manual describes as a hash state is an instance of this type.
Examples of hash states include the second argument and second return value of
object-hash.
- collection-hash Function#
Hashes the elements of a collection.
- Signature:
collection-hash key-hash-function elt-hash-function collection initial-state #key ordered => hash-id hash-state
- Parameters:
key-hash-function – An instance of
<function>.elt-hash-function – An instance of
<function>.collection – An instance of
<collection>.initial-state – An instance of
<hash-state>.ordered (#key) – An instance of
<boolean>. Default value:#f.
- Values:
hash-id – An instance of
<integer>.result-state – An instance of
<hash-state>.
- Discussion:
Hashes every element of collection using key-hash-function on the keys and elt-hash-function on the elements, and merges the resulting hash codes in order.
The ordered keyword is passed on to
merge-hash-ids.The functions key-hash-function and elt-hash-function must be suitable for use as hash functions. See page
123 of the DRM.
- sequence-hash Function#
Hashes the elements of a sequence.
- Signature:
sequence-hash elt-hash-function sequence initial-state #key ordered => hash-id result-state
- Parameters:
elt-hash-function – An instance of
<function>.sequence – An instance of
<sequence>.initial-state – An instance of
<hash-state>.ordered (#key) – An instance of
<boolean>. Default value:#f.
- Values:
hash-id – An instance of
<integer>.result-state – An instance of
<hash-state>.
- Discussion:
Hashes every element of sequence using elt-hash-function, and merges the resulting hash codes in order.
The function elt-hash-function must be suitable for use as a hash function. See page
123 of the DRM.The ordered keyword is passed on to
merge-hash-ids.
- values-hash Function#
Hashes the values passed to it.
- Signature:
values-hash elt-hash-function initial-state #rest arguments => hash-id result-state
- Parameters:
elt-hash-function – An instance of
<function>.hash-state – An instance of
<hash-state>.initial-state – An instance of
<hash-state>.arguments (#rest) – Instances of
<object>.
- Values:
hash-id – An instance of
<integer>.result-state – An instance of
<hash-state>.
- Discussion:
Hashes every object in arguments using elt-hash-function, and merges the resulting hash codes in order.
The function elt-hash-function must be suitable for use as a hash function. See page
123 of the DRM.The ordered keyword is passed on to
merge-hash-ids.
- string-hash Function#
Hashes a string.
- Signature:
string-hash string initial-state => hash-id result-state
- Parameters:
string – An instance of
<string>.initial-state – An instance of
<hash-state>.
- Values:
hash-id – An instance of
<integer>.result-state – An instance of
<hash-state>.
- Discussion:
Produces a hash code for a string, using the equivalence predicate
\=.
- case-insensitive-string-hash Function#
Hashes a string, without considering case information.
- Signature:
case-insensitive-string-hash string initial-state => hash-id result-state
- Parameters:
string – An instance of
<string>.initial-state – An instance of
<hash-state>.
- Values:
hash-id – An instance of
<integer>.result-state – An instance of
<hash-state>.
- Discussion:
Produces a hash code for a string using the equivalence predicate
case-insensitive-equal, which does not consider the case of the characters in the strings it compares.- See also:
- case-insensitive-equal Function#
Compares two strings for equality, ignoring case differences between them.
- Signature:
case-insensitive-equal string1 string2 => boolean
- Parameters:
- Values:
boolean – An instance of
<boolean>.
- Discussion:
Compares string1 and string2 for equality, ignoring any case differences between them. Returns true if they are equal and false otherwise.
The function has the same behavior as Dylan’s standard method on = for sequences, except that when comparing alphabetical characters, it ignores any case differences.
This function is used as an equivalence predicate by
case-insensitive-string-hash.This function uses as-uppercase or as-lowercase to convert the characters in its string arguments.
- Example:
The case-insensitive-equal function returns true if passed the following strings:
"The Cat SAT ON the Mat" "The cat sat on the Mat"
Conversely, the standard method on = returns false when passed those strings.
- See also:
- remove-all-keys! Open Generic function#
Removes all keys from a collection and leaves it empty.
- Signature:
remove-all-keys! collection => collection
- Parameters:
collection – An instance of
<mutable-explicit-key-collection>.
- Values:
collection – An instance of
<mutable-explicit-key-collection>.
- Discussion:
Modifies collection by removing all its keys and elements, and leaves it empty.
Note
To empty collections that are not instances of
<mutable-explicit-key-collection>, use size-setter.
- remove-all-keys!(<mutable-explicit-key-collection>) Method#
Removes all keys from a collection and leaves it empty.
- Signature:
remove-all-keys! collection => collection
- Parameters:
collection – An instance of
<mutable-explicit-key-collection>.
- Values:
collection – An instance of
<mutable-explicit-key-collection>.
- Discussion:
Modifies collection by removing all its keys and elements, and leaves it empty. This method implements the generic function by making repeated calls to
remove-key!.Note
To empty collections that are not instances of
<mutable-explicit-key-collection>, use size-setter.
- remove-all-keys!(<table>) Method#
Removes all keys from a table and leaves it empty.
- Signature:
remove-all-keys! table => table
- Parameters:
- Discussion:
Modifies table by removing all its keys and elements, and leaves it empty.
This method does not use
remove-key!.Note
To empty collections that are not instances of
<mutable-explicit-key-collection>, use size-setter.
- tabling Function Macro#
Creates a table and populates it with keys and values.
- Macro Call:
tabling( [ class, ] key => value, ...)
- Parameters:
class – An instance of
<class>. Optional.key – An expression.
value – An expression.
- Values:
table – A new instance of class.
- Discussion:
Creates a table of type class and populates it with key/value pairs. If class is omitted, creates a table of type
<table>.- Example:
let my-table = tabling(#"red" => "stop", #"green" => "go"); let my-table = tabling(<string-table>, "red" => "stop", "green" => "go");