metaitem.md

MetaItem

• Overview
• Header
• MetaItem member functions
  • getType
  • isEmpty
  • getName
  • asXxx functions
  • getTarget
  • Implicitly type convert
  • registerAnnotation
  • getAnnotation
  • getAllAnnotations

Overview

MetaItem represents the meta data registered in MetaRepo and MetaClass.
When registering any meta data in MetaRepo and MetaClass, the register function returns a MetaItem.
When retrieving any meta data from MetaRepo and MetaClass, the returned data is either MetaItem or MetaItemView.

Header

#include "metapp/metaitem.h"

MetaItem member functions

getType

MetaItem::Type getType() const;

Returns the type of the MetaItem. Each MetaItem has one type.
MetaItem::Type is a enum class.

enum class MetaItem::Type {
  none,
  accessible,
  callable,
  variable,
  constructor,
  metaRepo,
  metaType,
  enumValue
};

The values,

MetaItem::Type::none
The item doesn't have any valid type. isEmpty() will return true.
Don't check this type, use isEmpty() instead.

MetaItem::Type::accessible
The item is an accessible that implements MetaAccessible meta interface.

MetaItem::Type::callable
The item is a callable that implements MetaCallable meta interface.

MetaItem::Type::variable
The item is a variable.

MetaItem::Type::constructor
The item is a constructor.

MetaItem::Type::metaRepo
The item is a MetaRepo.

MetaItem::Type::metaType
The item is a MetaType.

MetaItem::Type::enumValue
The item is a value in MetaEnum.

isEmpty

bool isEmpty() const;

Returns true if the item doesn't hold any valid data.

getName

const std::string & getName() const

Returns the name. If the item doesn't have name, returns empty string.
MetaItem::Type::constructor always has empty name.

asXxx functions

const Variant & asAccessible() const;
const Variant & asCallable() const;
const Variant & asVariable() const;
const Variant & asConstructor() const;
const MetaType * asMetaType() const;
const MetaRepo * asMetaRepo() const;
const Variant & asEnumValue() const;

Returns the proper data.
If the type doesn't match the function, exception metapp::WrongMetaTypeException is raised.

getTarget

const Variant & getTarget() const;

Return the underlying Variant of the meta item. It doesn't check if the type matches, and it doesn't convert the data to appropriate type such as const MetaRepo *.

Implicitly type convert

operator const Variant & () const;

Convert the item to Variant implicitly. This is useful to pass the meta item where a Variant is required. For example,

metapp::MetaRepo metaRepo;
metaRepo.registerCallable("funcForMetaItem", std::function<int()>([]() {
  return 5;
}));
const metapp::MetaItem & callable = metaRepo.getCallable("funcForMetaItem");

The first argument in metapp::callableInvoke is metapp::Variant, we can pass metapp::MetaItem to it the item will convert to metapp::Variant.

const metapp::Variant result = metapp::callableInvoke(callable, nullptr);
ASSERT(result.get<int>() == 5);

We can also get the Variant from the item explicitly

const metapp::Variant result2 = metapp::callableInvoke(callable.asCallable(), nullptr);
ASSERT(result2.get<int>() == 5);

registerAnnotation

void registerAnnotation(const std::string & name, const Variant & value);

Register an annotation value under name.
An annotation is any data. metapp doesn't use the data.
The user can use the annotation for any purpose. For example, if metapp is used in a property editor, an annotation may provide description, or indicate a property should be hidden from the editor.

getAnnotation

const Variant & getAnnotation(const std::string & name) const;

Returns the annotation for name. If name is not registered, an empty Variant is returned (Variant::isEmpty() is true).

getAllAnnotations

const std::map<std::string, Variant> & getAllAnnotations() const;

Returns all registered annotations in a std::map.