7.13.6 Class and Interface Clause Macros
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The compile-time body block returns the expansion result. The result must be a sequence of groups to be spliced in place of the macro use, where each group can be either a another class clause, an expression, a defintion, or an export.
In addition to an ~op_stx option like defn.macro, the optional ~info body form binds an id to a class_meta.Info value. Use the class_meta.Info.lookup function to access information about the class declaration that appears before the use of the class-clause macro.
'private field result: #false
result := v
v)'
> class Person(name):
lazy_method greeting():
"Hello, " +& name
> ming.greeting()
"Hello, Ming"
#true
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Returns an object containing information about name, which must be bound as a class name or internal class name for class_meta.describe or as an interface name or internal interface name for interface_meta.describe. Use class_meta.Info.lookup or interface_meta.Info.lookup to extract details from the information object.
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A value satisfying class_meta.Info can be obtained from class_meta.describe or recieved by a class-clause macro through an ~info declaration. Similarly, a value satisfying interface_meta.Info can be obtained by interface_meta.describe or recieved by a interface-clause macro through an ~info declaration. In a macro declared with class_and_interface_clause.macro, a value received by ~info is an instance of either class_meta.Info or interface_meta.Info, which indicates the context where the macro is used.
info.lookup(key)
is
class_meta.Info.lookup(info, key)
info.lookup(key)
is
interface_meta.Info.lookup(info, key)
The class_meta.Info.lookup and interface_meta.Info.lookup functions access information via a key symbol. The currently recognized keys are described below, but more may be added in the future.
When receieved within a class-clause or interface-clause macro, the information reported for a key covers only class and interface clauses before the macro use, so a use of the same key in the same class but in a later clause may report different information. Furthermore, the information has not been fully checked; for example, the name of a class or interface being extended is reported as it appears, and has not yet been checked to be a valid class or interface name, and multiple names may be reported if a class contains multiple extends clauses. Similarly, field- or method-name lists may include duplicates.
When obtained via class_meta.describe or interface_meta.describe, the information covers the whole body of the referenced class or interface form. When a class or interface name is used, then information about private fields and methods is omitted from queries; using an internal name for a class or interface includes information about private fields and methods. A class- or inteface-clause macro, which directly receives only partial information, can expand to a use of an expression macro that uses class_meta.describe or interface_meta.describe to get more information based on a retained or newly declared internal name.
Reocgnized keys for classes:
#'name: An identifier for the defined class, including any dotted-name prefix in the class declaration.
#'extends: A list of indentifiers for classes declared as superclasses. Normally, the list will be empty or have one element, but a multi-identifier list can be reported for a clause macro if a class form has multiple extends clauses (even though an error will be reported later).
#'implements: A list of indentifiers for interfaces declared to be implemented by the class. The list does not include interfaces that are implied by superclasses and implemented interfaces. For a clause macro or starting from class_meta.describe with a class internal name, the list includes privately implemented interfaces.
#'implements_visibilities: A list of symbols in parallel to a #'implements list that categorizes each implementation’s visibility: #'public or #'private.
#'internal_names: A list of identifiers declared as internal names for this class. This list will be non-empty only in the information provided to a clause macro.
#'field_names: A list of identifiers for fields declared for the class in the order of the field declarations. For a clause macro, the list does not include fields that will be inherited from a superclass, while inherited public fields are included in information obtained via class_meta.describe.
#'field_mutabilities: A list of symbols in parallel to a #'field_names list that categorizes each field’s mutability: #'immutable or #'immutable.
#'field_visibilities: A list of symbols in parallel to a #'field_names list that categorizes each field’s visibility: #'public or #'private.
#'field_constructives: A list of symbols in parallel to a #'field_names list that categorizes each field’s use in the default constructor: #'required, #'optional, or #'absent. All private fields are classified as #'absent.
#'field_keywords: A list of keywords and #falses in parallel to a #'field_names, where a keyword indicates that the field uses that keyword as an argument for the default constructor.
#'method_names: A list of identifiers for methods declared for the class in the order of the method declarations. The list does not include methods that will be inherited from a superclass or implemented interface, while inherited public methods are included in information obtained via class_meta.describe.
#'method_visibilities: A list of symbols in parallel to a #'methods_names list that categorizes each methods’s visibility: #'public or #'private.
#'method_arities: A list of arity representations in parallel to a #'methods_names list. An arity represenation can be an integer, in which case each bit set in the integer represents a number of arguments accepted by the method, and no keyword argument are accepted. An arity represenation can be a list, in which case the first element is an integer (like an integer by itself), the second element is a list of required keywords for arguments, and the last element is either a list of allowed keywords or #false if all keywords are accepted. An arity representation can be #false if no information about accepted arguments is available. Keep in mind that when a subclass overrides a method, it is not limited to the existing method’s arity.
#'property_names: A list of identifiers for properties declared for the class in the order of the property declarations. The list does not include properties that will be inherited from a superclass or implemented interface, while inherited public properties are included in information obtained via class_meta.describe.
#'property_visibilities: A list of symbols in parallel to a #'property_names list that categorizes each property’s visibility: #'public or #'private.
#'property_arities: A list of arity representations in parallel to a #'property_names list. An arity representation is 1 if the property does not support assignent, 3 if it does support assignment, or #false if the property’s support for assignments is unknown.
#'uses_default_constructor: A boolean indicating whether the class name in an expression position refers to a default constructor function.
#'uses_default_binding: A boolean indicating whether the class name in a binding position refers to a default binding form.
#'uses_default_annotation: A boolean indicating whether the class name in an annotation position refers to a default annotation form.
Reocgnized keys for interfaces:
#'name: An identifier for the interface being defined, including any dotted-name prefix in the interface declaration.
#'extends: A list of indentifiers for interfaces declared as superinterfaces. The list does not include interfaces that are implied by superinterfaces.
#'internal_names: The same as for classes.
#'method_names: The same as for classes.
#'method_arities: The same as for classes.
#'method_visibilities: The same as for classes.
#'property_names: The same as for classes.
#'property_arities: The same as for classes.
#'property_visibilities: The same as for classes.
#'uses_default_annotation: A boolean indicating whether the interface name in an annotation position refers to a default annotation form.