qapi: Improve qobject visitor documentation

/*

 * Input Visitor

 *

 * Copyright (C) 2017 Red Hat, Inc.

 * Copyright IBM, Corp. 2011

 *

 * Authors:

typedef struct QObjectInputVisitor QObjectInputVisitor;

/*

 * Return a new input visitor that converts a QObject to a QAPI object.

 * Create a QObject input visitor for @obj

 *

 * A QObject input visitor visit builds a QAPI object from a QObject.

 * This simultaneously walks the QAPI object being built and the

 * QObject.  The latter walk starts at @obj.

 *

 * visit_type_FOO() creates an instance of QAPI type FOO.  The visited

 * QObject must match FOO.  QDict matches struct/union types, QList

 * matches list types, QString matches type 'str' and enumeration

 * types, QInt matches integer types, QFloat matches type 'number',

 * QBool matches type 'bool'.  Type 'any' is matched by QObject.  A

 * QAPI alternate type is matched when one of its member types is.

 *

 * visit_start_struct() ... visit_end_struct() visits a QDict and

 * creates a QAPI struct/union.  Visits in between visit the

 * dictionary members.  visit_optional() is true when the QDict has

 * this member.  visit_check_struct() fails if unvisited members

 * remain.

 *

 * visit_start_list() ... visit_end_list() visits a QList and creates

 * a QAPI list.  Visits in between visit list members, one after the

 * other.  visit_next_list() returns NULL when all QList members have

 * been visited.  visit_check_list() fails if unvisited members

 * remain.

 *

 * visit_start_alternate() ... visit_end_alternate() visits a QObject

 * and creates a QAPI alternate.  The visit in between visits the same

 * QObject and initializes the alternate member that is in use.

 *

 * Error messages refer to parts of @obj in JavaScript/Python syntax.

 * For example, 'a.b[2]' refers to the second member of the QList

 * member 'b' of the QDict member 'a' of QDict @obj.

 *

 * The caller is responsible for freeing the visitor with

 * visit_free().

 */

Visitor *qobject_input_visitor_new(QObject *obj);

typedef struct QObjectOutputVisitor QObjectOutputVisitor;

/*

 * Create a new QObject output visitor.

/**

 * Create a QObject output visitor for @obj

 *

 * A QObject output visitor visit builds a QObject from QAPI Object.

 * This simultaneously walks the QAPI object and the QObject being

 * built.  The latter walk starts at @obj.

 *

 * visit_type_FOO() creates a QObject for QAPI type FOO.  It creates a

 * QDict for struct/union types, a QList for list types, QString for

 * type 'str' and enumeration types, QInt for integer types, QFloat

 * for type 'number', QBool for type 'bool'.  For type 'any', it

 * increments the QObject's reference count.  For QAPI alternate

 * types, it creates the QObject for the member that is in use.

 *

 * visit_start_struct() ... visit_end_struct() visits a QAPI

 * struct/union and creates a QDict.  Visits in between visit the

 * members.  visit_optional() is true when the struct/union has this

 * member.  visit_check_struct() does nothing.

 *

 * visit_start_list() ... visit_end_list() visits a QAPI list and

 * creates a QList.  Visits in between visit list members, one after

 * the other.  visit_next_list() returns NULL when all QAPI list

 * members have been visited.  visit_check_list() does nothing.

 *

 * visit_start_alternate() ... visit_end_alternate() visits a QAPI

 * alternate.  The visit in between creates the QObject for the

 * alternate member that is in use.

 *

 * Errors are not expected to happen.

 *

 * If everything else succeeds, pass @result to visit_complete() to

 * collect the result of the visit.

 * The caller is responsible for freeing the visitor with

 * visit_free().

 */

Visitor *qobject_output_visitor_new(QObject **result);