core::PropertySetVariant< TAG > Class Template Reference

A variant type (tagged-union) with PropertySet fields. More...

#include <properties.h>

Inheritance diagram for core::PropertySetVariant< TAG >:

Public Member Functions
TAG	tag () const
	The tag value indicating the active PropertySet case.
void	selectCase (TAG tag)
	Selects the active PropertySet case.
const PropertySet *	activeCase () const
	Returns the active PropertySet.
PropertySet *	activeCase ()
	Returns the active PropertySet.
json	toJson () const
	Serialize to a json object. More...
void	fromJson (const json &json_obj)
	Deserialize from a json object. More...
void	copyFrom (const PropertySetVariant &src)
	Transfer values between two property set variants.

Detailed Description

template<class TAG>
class core::PropertySetVariant< TAG >

A variant type (tagged-union) with PropertySet fields.

The PropertySetVariant offers a simple solution for grouping a set of mutually exclusive property sets. The tag type (normally an enum) tracks which field (case) is active.

Defining variants

First, we need a scalar tag type:

enum class VariantTag {
  Empty,
  Basic,
  Extra,
};

// the tag type must support core::toString() and core::fromString()
inline auto customStringify(core::TypeTag<VariantTag>) {
  static auto stringify = new core::StringifyKnownValues<VariantTag>{
    { VariantTag::Empty, "empty" },
    { VariantTag::Basic, "basic" },
    { VariantTag::Extra, "extra" },
  };
  return stringify;
}

The variant type must derive from PropertySetVariant, and the CASE(tag, name, type) macro is used to declare the variant fields (cases):

struct VariantType : public core::PropertySetVariant<VariantTag> {
  CASE(VariantTag::Empty, empty, EmptyProperties);
  CASE(VariantTag::Basic, basic, BasicProperties);
  CASE(VariantTag::Extra, extra, ExtraProperties);
};

Finally, the variant type is intended to be used inside a PropertySet, using the VARIANT(name, type, default_case, description) macro to declare variant fields.

struct Properties : public core::PropertySet {
  ...
  VARIANT(name, VariantType, VariantTag::Basic, "A variant property");
  ...
};

See also

PropertySet

Member Function Documentation

fromJson()

template<class TAG>

void core::PropertySetVariant< TAG >::fromJson ( const json &  json_obj )

inline

Deserialize from a json object.

The deserialization is not strict:

• Extra cases are ignored
• Missing cases will be set to the default values

toJson()

template<class TAG>

json core::PropertySetVariant< TAG >::toJson ( ) const

inline

Serialize to a json object.

Note

All the PropertySet cases are serialized, not just the active one

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The documentation for this class was generated from the following file:

• C:/Users/lemo/work/darwin/core/properties.h