Macro

Summary

Used to simplify reference counting when querying a COM interface pointer.

Package

com

Signature

with-query-interface disp interface-ptr form* => values

disp ::= (punknown interface-name &key errorp dispatch)

Arguments

punknown

A variable which is bound to the queried interface pointer while the forms are evaluated.

interface-name

A symbol which names the COM interface. It is not evaluated.

errorp

A boolean indicating whether an error should be signaled if interface-name is not implemented by interface-ptr.

dispatch

A symbol which will be defined as a local macro, as if by macrolet as if by with-com-interface. The macro can be used by the forms to invoke the methods on punknown.

interface-ptr

A form which is evaluated to yield a COM interface pointer to query.

form

A form to be evaluated.

Values

values

The values returned by the last form.

Description

The macro with-query-interface calls query-interface to find an interface pointer for interface-name from the existing COM interface pointer interface-ptr. While evaluates the forms, the variable punknown is bound to the queried pointer and the pointer is released when control leaves the body (whether directly or due to a non-local exit).

If errorp is true, then punknown is bound to nil if the interface pointer cannot be found, otherwise an error of type com-error is signaled.

If dispatch is specified, then a local macro is created as if by with-com-interface to invoke COM interface methods on punknown.

Example

This example invokes the methods on an i-bar interface pointer queried from an existing interface pointer.

(with-query-interface (p-bar i-bar

                       :dispatch call-bar)

    p-foo

  (call-bar bar-init)

  (call-bar bar-print))

See also

query-interface
release
with-temp-interface