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![]() | Pack logtalk -- logtalk-3.81.0/manuals/_sources/libraries/options.rst.txt |
.. _library_options:
options
This library provides useful predicates for managing developer tool and application options.
Open the `../../docs/library_index.html#options <../../docs/library_index.html#options>`__ file in a web browser.
To load all entities in this library, load the loader.lgt
utility
file:
::
| ?- logtalk_load(options(loader))
.
To test this library predicates, load the tester.lgt
file:
::
| ?- logtalk_load(options(tester))
.
The options
category is usually imported by the root object of the
developer tool or application. The importing object should define the
default_option/1 predicate and, if option type-checking is required,
the valid_option/1 predicate must be defined for each option. This
library requires options to be represented by compound terms where the
functor is the option name (e.g. trim(true)
or (box(0,2)
)). The
option/2-3
can be used to get or test an option given a list of
options. When an option appears multiple times in a list, the
option/2-3
predicates get or test the first (leftmost) occurrence.
The library also supports a user-defined fix_option/2 predicate. An usage example is when an option value can be a relative file path that should be expanded before used. Another usage example would be converting from a user-friendly option to a form more suitable for internal processing. When a call to the fix_option/2 predicate fails, the option is used as-is.
A simple example:
::
:- object(foo,
imports(options))
.
:- uses(type, [
valid/2
])
.
:- public(p/0)
.
p :-
% use default options
p([])
.
:- public(p/1)
.
p(UserOptions)
:-
^^check_options(UserOptions)
,
% construct the full set of options from
% the user options and the default options
^^merge_options(UserOptions, Options)
,
...
% query an option
^^option(baz(Boolean), Options)
,
q(Boolean)
,
...
default_option(baz(true))
.
...
valid_option(baz(Boolean))
:-
valid(boolean, Boolean)
.
...
:- end_object.
Note that you can use protected or private import of the options
category if you don't want to add its public predicates to the object
protocol.