Question: Can Delphi be used with Ruby?

Reflection (computer programming)


Programming paradigms
Action
Agent-oriented
Array-oriented
Automata-based
Concurrent computing
Relativistic programming
Data-driven
Declarative (contrast: Imperative)
Functional
Functional logic
Purely functional
Logic
Abductive logic
Answer set
Concurrent logic
Functional logic
Inductive logic
Constraint
Constraint logic
Concurrent constraint logic
Dataflow
Flow-based
Reactive
Ontology
Differentiable
Dynamic/scripting
Event-driven
Function-level (contrast: Value-level)
Point-free style
Concatenative
Generic
Imperative (contrast: Declarative)
Procedural
Object-oriented
Polymorphic
Intentional
Language-oriented
Domain-specific
Literate
Natural-language programming
Metaprogramming
Automatic
Inductive programming
Reflective
Attribute-oriented
Macro
Template
Non-structured (contrast: Structured)
Array
Nondeterministic
Parallel computing
Process-oriented
Probabilistic
Quantum
Stack-based
Structured (contrast: Non-structured)
Block-structured
Object-oriented
Actor-based
Class-based
Concurrent
Prototype-based
By separation of concerns:
Aspect-oriented
Role-oriented
Subject-oriented
Recursive
Symbolic
Value-level (contrast: Function-level)vt
In computer science, reflection is the ability of a computer program to examine, introspect, and modify its own structure and behavior at runtime.[1]
Historical background
The earliest computers were programmed in their native assembly language, which were inherently reflective, as these original architectures could be programmed by defining instructions as data and using self-modifying code. As programming moved to compiled higher-level languages such as Algol, Cobol, and Fortran (but also Pascal and C and many other languages), this reflective ability largely disappeared until programming languages with reflection built into their type systems appeared.
Brian Cantwell Smith's 1982 doctoral dissertation[2][3] introduced the notion of computational reflection in procedural programming languages and the notion of the meta-circular interpreter as a component of 3-Lisp.
Uses
Reflection helps programmers make generic software libraries to display data, process different formats of data, perform serialization or deserialization of data for communication, or do bundling and unbundling of data for containers or bursts of communication.
Effective use of reflection almost always requires a plan: A design framework, encoding description, object library, a map of a database or entity relations.
Reflection makes a language more suited to network-oriented code. For example, it assists languages such as Java to operate well in networks by enabling libraries for serialization, bundling and varying data formats. Languages without reflection (e.g. C) have to use auxiliary compilers, e.g. for Abstract Syntax Notation, to produce code for serialization and bundling.
Reflection can be used for observing and modifying program execution at runtime. A reflection-oriented program component can monitor the execution of an enclosure of code and can modify itself according to a desired goal related to that enclosure. This is typically accomplished by dynamically assigning program code at runtime.
In object-oriented programming languages such as Java, reflection allows inspection of classes, interfaces, fields and methods at runtime without knowing the names of the interfaces, fields, methods at compile time. It also allows instantiation of new objects and invocation of methods.
Reflection is often used as part of software testing, such as for the runtime creation/instantiation of mock objects.
Reflection is also a key strategy for metaprogramming.
In some object-oriented programming languages, such as C# and Java, reflection can be used to override member accessibility rules. For example, reflection makes it possible to change the value of a field marked "private" in a third-party library's class.
Implementation

A language supporting reflection provides a number of features available at runtime that would otherwise be difficult to accomplish in a lower-level language. Some of these features are the abilities to:
Discover and modify source-code constructions (such as code blocks, classes, methods, protocols, etc.) as first-class objects at runtime.
Convert a string matching the symbolic name of a class or function into a reference to or invocation of that class or function.
Evaluate a string as if it were a source-code statement at runtime.
Create a new interpreter for the language's bytecode to give a new meaning or purpose for a programming construct.
These features can be implemented in different ways. In MOO, reflection forms a natural part of everyday programming idiom. When verbs (methods) are called, various variables such as verb (the name of the verb being called) and this (the object on which the verb is called) are populated to give the context of the call. Security is typically managed by accessing the caller stack programmatically: Since callers() is a list of the methods by which the current verb was eventually called, performing tests on callers()[1] (the command invoked by the original user) allows the verb to protect itself against unauthorised use.
Compiled languages rely on their runtime system to provide information about the source code. A compiled Objective-C executable, for example, records the names of all methods in a block of the executable, providing a table to correspond these with the underlying methods (or selectors for these methods) compiled into the program. In a compiled language that supports runtime creation of functions, such as Common Lisp, the runtime environment must include a compiler or an interpreter.
Reflection can be implemented for languages not having built-in reflection facilities by using a program transformation system to define automated source-code changes.
Examples
The following code snippets create an instance foo of class Foo and invoke its method PrintHello. For each programming language, normal and reflection-based call sequences are shown.
C#
The following is an example in C#:// Without reflection
Foo 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);

Delphi
This Delphi example assumes that a TFoo class has been declared in a unit called Unit1:
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;

This is a notable example, since Delphi is an unmanaged, fully natively compiled language, unlike most other languages that support reflection. Its language architecture inherits from strongly typed Pascal, but with significant influence from Smalltalk. Compare with the other examples here, many of which are dynamic or script languages like Perl, Python or PHP, or languages with a runtime like Java or C#.
eC
The following is an example in 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);

ECMAScript
The following is an example in ECMAScript, and therefore also applies to JavaScript and ActionScript:
// Without reflection
new Foo().hello()

// With reflection

// assuming that Foo resides in this
new this['Foo']()['hello']()

// or without assumption
new (eval('Foo'))()['hello']()

// or simply
eval('new Foo().hello()')

// Using ECMAScript 2015's new Reflect class:
Reflect.construct(Foo, [])['hello']()

Go
The following is an example in 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)
}

Java
The following is an example in Java:
// Without reflection
Foo foo = new Foo();
foo.hello();

// With reflection
Object foo = Class.forName("complete.classpath.and.Foo").newInstance();

// Alternatively: Object foo = Foo.class.newInstance();
Method m = foo.getClass().getDeclaredMethod("hello", new Class<?>[0]);
m.invoke(foo);

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

Perl
The following is an example in 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;";

PHP
The following is an example in 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);

Python
The following is an example in Python:
# without reflection
obj = Foo()
obj.hello()

# with reflection
class_name = "Foo"
method = "hello"
obj = globals()[class_name]()
getattr(obj, method)()

# with eval
eval("Foo().hello()")

R
The following is an example in R:
# Without reflection, assuming foo() returns an S3-type object that has method "hello"
obj <- foo()
hello(obj)

# With reflection
the.class <- "foo"
the.method <- "hello"
obj <- do.call(the.class, list())
do.call(the.method, alist(obj))

Ruby
The following is an example in Ruby:
# without reflection
obj = Foo.new
obj.hello

# with reflection
class_name = "Foo"
method_name = :hello
obj = Object.const_get(class_name).new
obj.send method_name

# with eval
eval "Foo.new.hello"

Xojo
The following is an example using Xojo:
' 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

See also
List of reflective programming languages and platforms
Mirror (programming)
Programming paradigms
Self-hosting
Self-modifying code
Type introspection

Notes

Documents
Jonathan M. Sobel and Daniel P. Friedman.  (1996), Indiana University.

Further reading
Ira R. Forman and Nate Forman, Java Reflection in Action (2005), ISBN1-932394-18-4
Ira R. Forman and Scott Danforth, Putting Metaclasses to Work (1999), ISBN0-201-43305-2




 from Oracle