API: Introduce value and datatype structs to Extern C

Summary

See #22 (closed). Introduce datatype and value structs to the Extern C interface which are then used to set and get property and entity values and datatypes. For this, an AbstractValue class was introduced to libcaosdb.

Focus

The former implementations of the caosdb_entity_{property,entity}_get_<type>_value functions have been replaced by the corresponding get functions that operate on value structs. In the same way, the former ..._{set,get}_datatype(char *, bool, bool) functions have been replaced by the corresponding caosdb_entity_datatype_is_<type> and caosdb_entity_datatype_get_datatype_name functions. The tests in test_ccaosdb have been adapted and extended.

Test Environment

Unit and integration tests should be sufficient.

Check List for the Author

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• All automated tests pass
• Reference related Issues
• Up-to-date CHANGELOG.md
• Annotations in code (Gitlab comments)
  • Intent of new code
  • Problems with old code
  • Why this implementation?

Check List for the Reviewer

• I understand the intent of this MR
• All automated tests pass
• Up-to-date CHANGELOG.md
• The test environment setup works and the intended behavior is reproducible in the test environment
• In-code documentation and comments are up-to-date.
• Check: Are there specifications? Are they satisfied?

For further good practices have a look at our review guidelines.

include/ccaosdb.h

@@ -419,6 +419,11 @@ int caosdb_entity_message_get_code(caosdb_entity_message *message, int *out);
 int caosdb_entity_message_get_description(caosdb_entity_message *message, char **out);
 
 // TODO(fspreck) getters for value and datatypes
+int caosdb_entity_datatype_is_atomic(caosdb_entity_datatype *datatype, bool *out);
+int caosdb_entity_datatype_is_reference(caosdb_entity_datatype *datatype, bool *out);
+int caosdb_entity_datatype_is_list_of_atomic(caosdb_entity_datatype *datatype, bool *out);
+int caosdb_entity_datatype_is_list_of_refernce(caosdb_entity_datatype *datatype, bool *out);
+
 int caosdb_entity_value_is_null(caosdb_entity_value *value, bool *out);
 int caosdb_entity_value_is_string(caosdb_entity_value *value, bool *out);
 int caosdb_entity_value_is_double(caosdb_entity_value *value, bool *out);
@@ -440,13 +445,14 @@ int caosdb_entity_create_property(caosdb_entity_property *out);
 int caosdb_entity_delete_property(caosdb_entity_property *out);
 int caosdb_entity_create_parent(caosdb_entity_parent *out);
 int caosdb_entity_delete_parent(caosdb_entity_parent *out);
-// TODO(fspreck) implementations, also list_datatypes, list_values...
+
 // DATATYPE CONSTRUCTORS for atomic and reference datatypes and lists thereof
 int caosdb_entity_create_atomic_datatype(caosdb_entity_datatype *out, const char *name);
 int caosdb_entity_create_reference_datatype(caosdb_entity_datatype *out, const char *name);
 int caosdb_entity_create_atomic_list_datatype(caosdb_entity_datatype *out, const char *name);
 int caosdb_entity_create_reference_list_datatype(caosdb_entity_datatype *out, const char *name);
 int caosdb_entity_delete_datatype(caosdb_entity_datatype *out);
+
 // VALUE CONSTRUCTORS (resolve overloaded constructors)
 int caosdb_entity_create_int_value(caosdb_entity_value *out, const int64_t value);
 int caosdb_entity_create_string_value(caosdb_entity_value *out, const char *value);