Reflection/List properties

Reflection/List properties
You are encouraged to solve this task according to the task description, using any language you may know.

Task

The goal is to get the properties of an object, as names, values or both.

Some languages support dynamic properties, which in general can only be inspected if a class' public API includes a way of listing them.

Java

<lang java>import java.lang.reflect.Field;

public class ListFields {

   public int examplePublicField = 42;
   private boolean examplePrivateField = true;
   
   public static void main(String[] args) throws IllegalAccessException {
       ListFields obj = new ListFields();
       Class clazz = obj.getClass();

       System.out.println("All public fields (including inherited):");
       for (Field f : clazz.getFields()) {
           System.out.printf("%s\t%s\n", f, f.get(obj));
       }
       System.out.println();
       System.out.println("All declared fields (excluding inherited):");
       for (Field f : clazz.getDeclaredFields()) {
           System.out.printf("%s\t%s\n", f, f.get(obj));
       }
   }

}</lang>

Output:

All public fields (including inherited):
public int ListFields.examplePublicField	42

All declared fields (excluding inherited):
public int ListFields.examplePublicField	42
private boolean ListFields.examplePrivateField	true

JavaScript

There are multiple ways of getting property names, each of which include different subsets of an object's properties, such as enumerable or inherited properties. Properties in JavaScript can be enumerable or non-enumerable; enumerable properties are accessable when looping over the object with for. Object.getOwnPropertyNames().

<lang javascript>var obj = Object.create({

   name: 'proto',
   proto: true,
   doNothing: function() {}
 }, {
   name: {value: 'obj', writable: true, configurable: true, enumerable: true},
   obj: {value: true, writable: true, configurable: true, enumerable: true},
   'non-enum': {value: 'non-enumerable', writable: true, enumerable: false},
   doStuff: {value: function() {}, enumerable: true}

});

// get enumerable properties on an object and its ancestors function get_property_names(obj) {

   var properties = [];
   for (var p in obj) {
       properties.push(p);
   }
   return properties;

}

get_property_names(obj); //["name", "obj", "doStuff", "proto", "doNothing"]

Object.getOwnPropertyNames(obj); //["name", "obj", "non-enum", "doStuff"]

Object.keys(obj); //["name", "obj", "doStuff"]

Object.entries(obj); //[["name", "obj"], ["obj", true], ["doStuff", function()]] </lang>

Lingo

<lang lingo>obj = script("MyClass").new() obj.foo = 23 obj.bar = 42

-- ...

-- show obj's property names and values cnt = obj.count repeat with i = 1 to cnt

 put obj.getPropAt(i)&" = "&obj[i]

end repeat</lang>

Output:

-- "bar = 42"
-- "foo = 23"

Objective-C

<lang objc>#import <Foundation/Foundation.h>

1. import <objc/runtime.h>

@interface Foo : NSObject {

 int exampleIvar;

} @property (nonatomic) double exampleProperty; @end @implementation Foo - (instancetype)init {

 self = [super init];
 if (self) {
   exampleIvar = 42;
   _exampleProperty = 3.14;
 }
 return self;

} @end

int main() {

 id obj = [[Foo alloc] init];
 Class clazz = [obj class];

 NSLog(@"\Instance variables:");
 unsigned int ivarCount;
 Ivar *ivars = class_copyIvarList(clazz, &ivarCount);
 for (unsigned int i = 0; i < ivarCount; i++) {
   Ivar ivar = ivars[i];
   const char *name = ivar_getName(ivar);
   const char *typeEncoding = ivar_getTypeEncoding(ivar);
   // for simple types we can use Key-Value Coding to access it
   // but in general we will have to use object_getIvar and cast it to the right type of function
   // corresponding to the type of the instance variable
   id value = [obj valueForKey:@(name)];
   NSLog(@"%s\t%s\t%@", name, typeEncoding, value);
 }
 free(ivars);

 NSLog(@"");
 NSLog(@"Properties:");
 unsigned int propCount;
 objc_property_t *properties = class_copyPropertyList([Foo class], &propCount);
 for (unsigned int i = 0; i < propCount; i++) {
   objc_property_t p = properties[i];
   const char *name = property_getName(p);
   const char *attributes = property_getAttributes(p);
   // for simple types we can use Key-Value Coding to access it
   // but in general we will have to use objc_msgSend to call the getter,
   // casting objc_msgSend to the right type of function corresponding to the type of the getter
   id value = [obj valueForKey:@(name)];
   NSLog(@"%s\t%s\t%@", name, attributes, value);
 }
 free(properties);

 return 0;

}</lang>

Output:

Instance variables:
exampleIvar	i	42
_exampleProperty	d	3.14

Properties:
exampleProperty	Td,N,V_exampleProperty	3.14

Perl 6

You can get a list of an object's attributes (instance variables) using .^attributes, which is part of the Meta Object Protocol..
Each is represented as an Attribute object that contains a bunch of info:

<lang perl6>class Foo {

   has $!a = now;
   has Str $.b;
   has Int $.c is rw;

}

my $object = Foo.new: b => "Hello", c => 42;

for $object.^attributes {

   say join ", ", .name, .readonly, .container.^name, .get_value($object);

}</lang>

Output:

$!a, True, Any, Instant:1470517602.295992
$!b, True, Str, Hello
$!c, False, Int, 42

Public attributes (in this case, $.b and $.c) are really just attributes for which the compiler also auto-generates a method of the same name. See Reflection/List_methods#Perl_6.

PHP

<lang php><? class Foo { } $obj = new Foo(); $obj->bar = 42; $obj->baz = true;

var_dump(get_object_vars($obj)); ?></lang>

Output:

array(2) {
  ["bar"]=>
  int(42)
  ["baz"]=>
  bool(true)
}

PowerShell

In PowerShell everything is an object. To find any type of member of any object use the Get-Member Cmdlet.

Here we find the properties of a [DateTime] object: <lang PowerShell> Get-Date | Get-Member -MemberType Property </lang>

Output:

   TypeName: System.DateTime

Name        MemberType Definition                       
----        ---------- ----------                       
Date        Property   datetime Date {get;}             
Day         Property   int Day {get;}                   
DayOfWeek   Property   System.DayOfWeek DayOfWeek {get;}
DayOfYear   Property   int DayOfYear {get;}             
Hour        Property   int Hour {get;}                  
Kind        Property   System.DateTimeKind Kind {get;}  
Millisecond Property   int Millisecond {get;}           
Minute      Property   int Minute {get;}                
Month       Property   int Month {get;}                 
Second      Property   int Second {get;}                
Ticks       Property   long Ticks {get;}                
TimeOfDay   Property   timespan TimeOfDay {get;}        
Year        Property   int Year {get;}                  

The "Add" methods of a [DateTime object: <lang PowerShell> Get-Date | Get-Member -MemberType Method -Name Add* </lang>

Output:

   TypeName: System.DateTime

Name            MemberType Definition                            
----            ---------- ----------                            
Add             Method     datetime Add(timespan value)          
AddDays         Method     datetime AddDays(double value)        
AddHours        Method     datetime AddHours(double value)       
AddMilliseconds Method     datetime AddMilliseconds(double value)
AddMinutes      Method     datetime AddMinutes(double value)     
AddMonths       Method     datetime AddMonths(int months)        
AddSeconds      Method     datetime AddSeconds(double value)     
AddTicks        Method     datetime AddTicks(long value)         
AddYears        Method     datetime AddYears(int value)          

Python

The dir() function and Python's inspect module both will list properties.

<lang python>class Parent(object):

   __priv = 'private'
   
   def __init__(self, name):
       self.name = name
   
   def __repr__(self):
       return '%s(%s)' % (type(self).__name__, self.name)
   
   def doNothing(self):
       pass

import re

class Child(Parent):

   # prefix for "private" fields
   __rePrivate = re.compile('^_(Child|Parent)__')
   # used when setting dynamic property values
   __reBleh = re.compile('\Wbleh$')
   @property
   def reBleh(self):
       return self.__reBleh
   
   def __init__(self, name, *args):
       super(Child, self).__init__(name)
       self.args = args
   
   def __dir__(self):
       myDir = filter(
           # filter out private fields
           lambda p: not self.__rePrivate.match(p),
           list(set( \
               sum([dir(base) for base in type(self).__bases__], []) \
               + type(self).__dict__.keys() \
               + self.__dict__.keys() \
           )))
       return myDir + map(
           # dynamic properties
           lambda p: p + '_bleh',
           filter(
               # don't add dynamic properties for methods and other special properties
               lambda p: (p[:2] != '__' or p[-2:] != '__') and not callable(getattr(self, p)),
               myDir))
   
   def __getattr__(self, name):
       if name[-5:] == '_bleh':
           # dynamic '_bleh' properties
           return str(getattr(self, name[:-5])) + ' bleh'
       if hasattr(super(Child, chld), '__getattr__'):
           return super(Child, self).__getattr__(name)
       raise AttributeError("'%s' object has no attribute '%s'" % (type(self).__name__, name))
   
   def __setattr__(self, name, value):
       if name[-5:] == '_bleh':
           # skip backing properties that are methods
           if not (hasattr(self, name[:-5]) and callable(getattr(self, name[:-5]))):
               setattr(self, name[:-5], self.reBleh.sub(, value))
       elif hasattr(super(Child, self), '__setattr__'):
           super(Child, self).__setattr__(name, value)
       elif hasattr(self, '__dict__'):
           self.__dict__[name] = value
   
   def __repr__(self):
       return '%s(%s, %s)' % (type(self).__name__, self.name, str(self.args).strip('[]()'))
   
   def doStuff(self):
       return (1+1.0/1e6) ** 1e6

par = Parent('par') par.parent = True dir(par)

1. ['_Parent__priv', '__class__', ..., 'doNothing', 'name', 'parent']

inspect.getmembers(par)

1. [('_Parent__priv', 'private'), ('__class__', <class '__main__.Parent'>), ..., ('doNothing', <bound method Parent.doNothing of <__main__.Parent object at 0x100777650>>), ('name', 'par'), ('parent', True)]

chld = Child('chld', 0, 'I', 'two') chld.own = "chld's own" dir(chld)

1. ['__class__', ..., 'args', 'args_bleh', 'doNothing', 'doStuff', 'name', 'name_bleh', 'own', 'own_bleh', 'reBleh', 'reBleh_bleh']

inspect.getmembers(chld)

1. [('__class__', <class '__main__.Child'>), ..., ('args', (0, 'I', 'two')), ('args_bleh', "(0, 'I', 'two') bleh"), ('doNothing', <bound method Child.doNothing of Child(chld, 0, 'I', 'two')>), ('doStuff', <bound method Child.doStuff of Child(chld, 0, 'I', 'two')>), ('name', 'chld'), ('name_bleh', 'chld bleh'), ('own', "chld's own"), ('own_bleh', "chld's own bleh"), ('reBleh', <_sre.SRE_Pattern object at 0x10067bd20>), ('reBleh_bleh', '<_sre.SRE_Pattern object at 0x10067bd20> bleh')]

</lang>

Ruby

<lang ruby>class Foo

 @@xyz = nil
 def initialize(name, age)
   @name, @age = name, age
 end
 def add_sex(sex)
   @sex = sex
 end

end

p foo = Foo.new("Angel", 18) #=> #<Foo:0x0000000305a688 @name="Angel", @age=18> p foo.instance_variables #=> [:@name, :@age] p foo.instance_variable_defined?(:@age) #=> true p foo.instance_variable_get(:@age) #=> 18 p foo.instance_variable_set(:@age, 19) #=> 19 p foo #=> #<Foo:0x0000000305a688 @name="Angel", @age=19> foo.add_sex(:woman) p foo.instance_variables #=> [:@name, :@age, :@sex] p foo #=> #<Foo:0x0000000305a688 @name="Angel", @age=19, @sex=:woman> foo.instance_variable_set(:@bar, nil) p foo.instance_variables #=> [:@name, :@age, :@sex, :@bar]

p Foo.class_variables #=> [:@@xyz] p Foo.class_variable_defined?(:@@xyz) #=> true p Foo.class_variable_get(:@@xyz) #=> nil p Foo.class_variable_set(:@@xyz, :xyz) #=> :xyz p Foo.class_variable_get(:@@xyz) #=> :xyz p Foo.class_variable_set(:@@abc, 123) #=> 123 p Foo.class_variables #=> [:@@xyz, :@@abc]</lang>

zkl

In zkl, properties are static read only informational data.

Every object has a "properties" method, which returns a list of property names [for that object]. <lang zkl>properties:=List.properties; properties.println(); List(1,2,3).property(properties[0]).println(); // get value List(1,2,3).Property(properties[0])().println(); // method that gets value List(1,2,3).BaseClass(properties[0]).println(); // another way to get value</lang>

Output:

L("size","isReadOnly","id","name","fullName","type","otype","oID","itype","typeID","properties","methods","vaultPath","numObjects","isThreadSafe","isContainer","createReturnsSelf")
L(24,32)
L(24,32)
L(24,32)