Editing Reflective programming (section)

==Examples==
The following code snippets create an [[instance (computer science)|instance]] {{code|foo}} of [[class (computer science)|class]] {{code|Foo}} and invoke its [[method (computer science)|method]] {{code|PrintHello}}. For each [[programming language]], normal and reflection-based call sequences are shown.

=== Common Lisp ===
The following is an example in [[Common Lisp]] using the [[Common Lisp Object System]]:

<syntaxhighlight lang="lisp">
(defclass foo () ())
(defmethod print-hello ((f foo)) (format T "Hello from ~S~%" f))

;; Normal, without reflection
(let ((foo (make-instance 'foo)))
  (print-hello foo))

;; With reflection to look up the class named "foo" and the method
;; named "print-hello" that specializes on "foo".
(let* ((foo-class (find-class (read-from-string "foo")))
       (print-hello-method (find-method (symbol-function (read-from-string "print-hello"))
                                        nil (list foo-class))))
  (funcall (sb-mop:method-generic-function print-hello-method)
           (make-instance foo-class)))
</syntaxhighlight>

=== C# ===
The following is an example in [[C Sharp (programming language)|C#]]:

<syntaxhighlight lang="c#">
// Without reflection
var foo = new Foo();
foo.PrintHello();

// With reflection
Object foo = Activator.CreateInstance("complete.classpath.and.Foo");
MethodInfo method = foo.GetType().GetMethod("PrintHello");
method.Invoke(foo, null);
</syntaxhighlight>

===Delphi, Object Pascal===
This [[Delphi (software)|Delphi]] and [[Object Pascal]] example assumes that a {{mono|TFoo}} class has been declared in a unit called {{mono|Unit1}}:

<syntaxhighlight lang="Delphi">
uses RTTI, Unit1;

procedure WithoutReflection;
var
  Foo: TFoo;
begin
  Foo := TFoo.Create;
  try
    Foo.Hello;
  finally
    Foo.Free;
  end;
end;

procedure WithReflection;
var
  RttiContext: TRttiContext;
  RttiType: TRttiInstanceType;
  Foo: TObject;
begin
  RttiType := RttiContext.FindType('Unit1.TFoo') as TRttiInstanceType;
  Foo := RttiType.GetMethod('Create').Invoke(RttiType.MetaclassType, []).AsObject;
  try
    RttiType.GetMethod('Hello').Invoke(Foo, []);
  finally
    Foo.Free;
  end;
end;
</syntaxhighlight>

===eC===
The following is an example in eC:

<syntaxhighlight lang=eC>
// Without reflection
Foo foo { };
foo.hello();

// With reflection
Class fooClass = eSystem_FindClass(__thisModule, "Foo");
Instance foo = eInstance_New(fooClass);
Method m = eClass_FindMethod(fooClass, "hello", fooClass.module);
((void (*)())(void *)m.function)(foo);
</syntaxhighlight>

===Go===
The following is an example in [[Go (programming language)|Go]]:

<syntaxhighlight lang="go">
import "reflect"

// Without reflection
f := Foo{}
f.Hello()

// With reflection
fT := reflect.TypeOf(Foo{})
fV := reflect.New(fT)

m := fV.MethodByName("Hello")
if m.IsValid() {
    m.Call(nil)
}
</syntaxhighlight>

===Java===
The following is an example in [[Java (programming language)|Java]]:
<syntaxhighlight lang="java">
import java.lang.reflect.Method;

// Without reflection
Foo foo = new Foo();
foo.hello();

// With reflection
try {
    Object foo = Foo.class.getDeclaredConstructor().newInstance();

    Method m = foo.getClass().getDeclaredMethod("hello", new Class<?>[0]);
    m.invoke(foo);
} catch (ReflectiveOperationException ignored) {}
</syntaxhighlight>

===JavaScript===
The following is an example in [[JavaScript]]:

<syntaxhighlight lang="javascript">
// Without reflection
const foo = new Foo()
foo.hello()

// With reflection
const foo = Reflect.construct(Foo)
const hello = Reflect.get(foo, 'hello')
Reflect.apply(hello, foo, [])

// With eval
eval('new Foo().hello()')
</syntaxhighlight>

===Julia===
The following is an example in [[Julia (programming language)|Julia]]:
<syntaxhighlight lang="julia-repl">
julia> struct Point
           x::Int
           y
       end

# Inspection with reflection
julia> fieldnames(Point)
(:x, :y)

julia> fieldtypes(Point)
(Int64, Any)

julia> p = Point(3,4)

# Access with reflection
julia> getfield(p, :x)
3
</syntaxhighlight>

===Objective-C===
The following is an example in [[Objective-C]], implying either the [[OpenStep]] or [[Foundation Kit]] framework is used:

<syntaxhighlight lang="ObjC">
// Foo class.
@interface Foo : NSObject
- (void)hello;
@end

// Sending "hello" to a Foo instance without reflection.
Foo *obj = [[Foo alloc] init];
[obj hello];

// Sending "hello" to a Foo instance with reflection.
id obj = [[NSClassFromString(@"Foo") alloc] init];
[obj performSelector: @selector(hello)];
</syntaxhighlight>

===Perl===
The following is an example in [[Perl]]:

<syntaxhighlight lang="perl">
# Without reflection
my $foo = Foo->new;
$foo->hello;

# or
Foo->new->hello;

# With reflection
my $class = "Foo"
my $constructor = "new";
my $method = "hello";

my $f = $class->$constructor;
$f->$method;

# or
$class->$constructor->$method;

# with eval
eval "new Foo->hello;";
</syntaxhighlight>

===PHP===
The following is an example in [[PHP]]:<ref>{{cite web |title=PHP: ReflectionClass - Manual |url=https://www.php.net/manual/en/class.reflectionclass.php |website=www.php.net}}</ref>

<syntaxhighlight lang="php">
// Without reflection
$foo = new Foo();
$foo->hello();

// With reflection, using Reflections API
$reflector = new ReflectionClass("Foo");
$foo = $reflector->newInstance();
$hello = $reflector->getMethod("hello");
$hello->invoke($foo);
</syntaxhighlight>

===Python===
The following is an example in [[Python (programming language)|Python]]:

<syntaxhighlight lang="python">
# Without reflection
obj = Foo()
obj.hello()

# With reflection
obj = globals()["Foo"]()
getattr(obj, "hello")()

# With eval
eval("Foo().hello()")
</syntaxhighlight>

===R===
The following is an example in [[R (programming language)|R]]:

<syntaxhighlight lang="r">
# Without reflection, assuming foo() returns an S3-type object that has method "hello"
obj <- foo()
hello(obj)

# With reflection
class_name <- "foo"
generic_having_foo_method <- "hello"
obj <- do.call(class_name, list())
do.call(generic_having_foo_method, alist(obj))
</syntaxhighlight>

===Ruby===
The following is an example in [[Ruby (programming language)|Ruby]]:

<syntaxhighlight lang="ruby">
# Without reflection
obj = Foo.new
obj.hello

# With reflection
obj = Object.const_get("Foo").new
obj.send :hello

# With eval
eval "Foo.new.hello"
</syntaxhighlight>

===Xojo===
The following is an example using [[Xojo]]:

<syntaxhighlight lang="vbnet">
' Without reflection
Dim fooInstance As New Foo
fooInstance.PrintHello

' With reflection
Dim classInfo As Introspection.Typeinfo = GetTypeInfo(Foo)
Dim constructors() As Introspection.ConstructorInfo = classInfo.GetConstructors
Dim fooInstance As Foo = constructors(0).Invoke
Dim methods() As Introspection.MethodInfo = classInfo.GetMethods
For Each m As Introspection.MethodInfo In methods
  If m.Name = "PrintHello" Then
    m.Invoke(fooInstance)
  End If
Next
</syntaxhighlight>