Available since 1.0 (source)
  • (gen-class & options)
When compiling, generates compiled bytecode for a class with the
given package-qualified :name (which, as all names in these
parameters, can be a string or symbol), and writes the .class file
to the *compile-path* directory.  When not compiling, does
nothing. The gen-class construct contains no implementation, as the
implementation will be dynamically sought by the generated class in
functions in an implementing Clojure namespace. Given a generated
class org.mydomain.MyClass with a method named mymethod, gen-class
will generate an implementation that looks for a function named by 
(str prefix mymethod) (default prefix: "-") in a
Clojure namespace specified by :impl-ns
(defaults to the current namespace). All inherited methods,
generated methods, and init and main functions (see :methods, :init,
and :main below) will be found similarly prefixed. By default, the
static initializer for the generated class will attempt to load the
Clojure support code for the class as a resource from the classpath,
e.g. in the example case, ``org/mydomain/MyClass__init.class``. This
behavior can be controlled by :load-impl-ns
 Note that methods with a maximum of 18 parameters are supported.
 In all subsequent sections taking types, the primitive types can be
referred to by their Java names (int, float etc), and classes in the
java.lang package can be used without a package qualifier. All other
classes must be fully qualified.
 Options should be a set of key/value pairs, all except for :name are optional:
 :name aname
 The package-qualified name of the class to be generated
 :extends aclass
 Specifies the superclass, the non-private methods of which will be
overridden by the class. If not provided, defaults to Object.
 :implements [interface ...]
 One or more interfaces, the methods of which will be implemented by the class.
 :init name
 If supplied, names a function that will be called with the arguments
to the constructor. Must return [ [superclass-constructor-args] state] 
If not supplied, the constructor args are passed directly to
the superclass constructor and the state will be nil
 :constructors {[param-types] [super-param-types], ...}
 By default, constructors are created for the generated class which
match the signature(s) of the constructors for the superclass. This
parameter may be used to explicitly specify constructors, each entry
providing a mapping from a constructor signature to a superclass
constructor signature. When you supply this, you must supply an :init
 :post-init name
 If supplied, names a function that will be called with the object as
the first argument, followed by the arguments to the constructor.
It will be called every time an object of this class is created,
immediately after all the inherited constructors have completed.
Its return value is ignored.
 :methods [ [name [param-types] return-type], ...]
 The generated class automatically defines all of the non-private
methods of its superclasses/interfaces. This parameter can be used
to specify the signatures of additional methods of the generated
class. Static methods can be specified with ^{:static true} in the
signature's metadata. Do not repeat superclass/interface signatures
 :main boolean
 If supplied and true, a static public main function will be generated. It will
pass each string of the String[] argument as a separate argument to
a function called (str prefix main).
 :factory name
 If supplied, a (set of) public static factory function(s) will be
created with the given name, and the same signature(s) as the

:state name
 If supplied, a public final instance field with the given name will be
created. You must supply an :init function in order to provide a
value for the state. Note that, though final, the state can be a ref
or agent, supporting the creation of Java objects with transactional
or asynchronous mutation semantics.
 :exposes {protected-field-name {:get name :set name}, ...}
 Since the implementations of the methods of the generated class
occur in Clojure functions, they have no access to the inherited
protected fields of the superclass. This parameter can be used to
generate public getter/setter methods exposing the protected field(s)
for use in the implementation.
 :exposes-methods {super-method-name exposed-name, ...}
 It is sometimes necessary to call the superclass' implementation of an
overridden method.  Those methods may be exposed and referred in 
the new method implementation by a local name.
 :prefix string
 Default: "-" Methods called e.g. Foo will be looked up in vars called
prefixFoo in the implementing ns.
 :impl-ns name
 Default: the name of the current ns. Implementations of methods will be 
looked up in this namespace.
 :load-impl-ns boolean
 Default: true. Causes the static initializer for the generated class
to reference the load code for the implementing namespace. Should be
true when implementing-ns is the default, false if you intend to
load the code via some other method.