def-foreign-type

Arguments: name definition

Defines name to be a user-defined foreign class with the given definition. name must either be a symbol or a list beginning with a symbol and followed by attributes (see below). definition is not evaluated and must be a foreign type description as described in The Syntax for Foreign Types in ftype.htm.

Like defclass, def-foreign-type returns the class metaobject. The class metaobject can also be retrieved in the usual way by find-class.

The def-foreign-type macro immediately defines the given class in the current Lisp. It also expands into a form that causes that type definition to be made when the resulting form is evaluated.

Note that when a new foreign type is defined in terms of one or more named previously defined foreign types, the new definition is expressed in terms of the current primitive definition of the named types. If the named types are subsequently re-defined, the new type definition will not change. Thus:

(def-foreign-type one (:struct (nil :int)))

(def-foreign-type two one)

(def-foreign-type one (:struct (nil (:array :int 4))))

The foreign type two is not affected by the redefinition of the foreign type one.

Only one attribute can be specified. It is:

For example:

(def-foreign-type (foostruct (:pack 1)) (:struct (x :char) (y :int)))

Would pack the integer right next to the character, without the normal 3 bytes of padding.

See ftype.htm for information on foreign types in Allegro CL and foreign-functions.htm for general information on foreign functions in Allegro CL.

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This page was not revised from the 8.1 page.
Created 2010.1.21.