&gt; Generally speaking, why does it exist?

It exists for autoboxing as Google suggests.

If you have code like this:

    Integer foo = 0;
    foo++;

Java internally makes this into this helper expression:

    Integer foo = 0;
    let int foo_helper = foo.intValue() in foo_helper++;

Source: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6614974

That expression obviously has no syntax representation, it&#39;s just an AST level transformation to simplify compilation.

This is called the let form and is used for &quot;abbreviating&quot;. 

On the other hand, in procedural languages this is called &quot;declaring a variable&quot; because the variable&#39;s &quot;value&quot; cell can mutate in procedure languages. (In functional languages, it&#39;s just an abbreviation and no different to just writing it out in the first place)

I can think of a lot of languages that use it in the source code the language user writes (Haskell, ML, Scheme, SBCL, Arc, ...), so not sure how you didn&#39;t see it yet... 

Or did you mean just in Java?

    let x = 2 in (x + 5)

Is shorthand for:

    (\x (x + 5)) 2

which will eventually be reduced to 

    (2 + 5)

where `\` is supposed to be lambda.

As for why it&#39;s in Java, not sure. What it&#39;s supposed to do is declare variables, so check whether it&#39;s used there.


I use this method to compress an image 

    if(bitmapObject.compress(Bitmap.CompressFormat.PNG, 100, fOut))
    {
        ... 
    }

But the image I get is much smaller ( in the dimension ) that was before the compress action. 

My application need to send the compressed image thru the network - so i want to send as less data as I can ... but I must to keep the original size of the image. 

Is there some other way to keep the original bitmap dimension with some compress ? 

How to make Bitmap compress without change the bitmap size?

[This][1] link from the Gson project seems to indicate that I would have to do something like the following for serializing a typed Map to JSON:


        public static class NumberTypeAdapter 
          implements JsonSerializer&lt;Number&gt;, JsonDeserializer&lt;Number&gt;,
    InstanceCreator&lt;Number&gt; {
    
        public JsonElement serialize(Number src, Type typeOfSrc, JsonSerializationContext
    context) {
          return new JsonPrimitive(src);
        }
    
        public Number deserialize(JsonElement json, Type typeOfT,
    JsonDeserializationContext context)
            throws JsonParseException {
          JsonPrimitive jsonPrimitive = json.getAsJsonPrimitive();
          if (jsonPrimitive.isNumber()) {
            return jsonPrimitive.getAsNumber();
          } else {
            throw new IllegalStateException(&quot;Expected a number field, but was &quot; + json);
          }
        }
    
        public Number createInstance(Type type) {
          return 1L;
        }
      }
    
      public static void main(String[] args) {
        Map&lt;String, Number&gt; map = new HashMap&lt;String, Number&gt;();    
        map.put(&quot;int&quot;, 123);
        map.put(&quot;long&quot;, 1234567890123456789L);
        map.put(&quot;double&quot;, 1234.5678D);
        map.put(&quot;float&quot;, 1.2345F);
        Type mapType = new TypeToken&lt;Map&lt;String, Number&gt;&gt;() {}.getType();
    
        Gson gson = new GsonBuilder().registerTypeAdapter(Number.class, new
    NumberTypeAdapter()).create();
        String json = gson.toJson(map, mapType);
        System.out.println(json);
        
        Map&lt;String, Number&gt; deserializedMap = gson.fromJson(json, mapType);
        System.out.println(deserializedMap);
      }

Cool and that works, but it seems like so much overhead (***a whole Type Adapter class?***). I have used other JSON libraries like JSONLib and they let you build a map in the following way:



    JSONObject json = new JSONObject();
    for(Entry&lt;String,Integer&gt; entry : map.entrySet()){
         json.put(entry.getKey(), entry.getValue());
    }

Or if I have a custom class something like the following:

    JSONObject json = new JSONObject();
    for(Entry&lt;String,MyClass&gt; entry : map.entrySet()){
	 JSONObject myClassJson =  JSONObject.fromObject(entry.getValue());
         json.put(entry.getKey(), myClassJson);
    }


The process is more manual, but requires way less code and doesn&#39;t have the overhead of haivng to create a custom Type Adapter for Number or in most cases ***for my own custom class***.


Is this the only way to serialize a map with Gson, or has anyone found a way that beats out what Gson recommends in the link above.


  [1]: http://code.google.com/p/google-gson/issues/detail?id=45


Gson: Is there an easier way to serialize a map

The Java compiler seems to have support for `let` expressions in `com.sun.tools.javac.tree.*` (look for `LetExpr`).

One comment in JCTree even mentions some syntax

    (let int x = 3; in x+2)

which of course is not accepted by the grammar of the language and rejected in an earlier compiler phase.

I&#39;m wondering about the origin of this construct, which I have never seen before.

Is it used internally by `javac` or is it synthesized by other tools? Is it maybe just an artifact from the very early days of Java from a language feature which never saw the light?

Is there anything useful which can be done with it today?

*Generally speaking, why does it exist?*


Purpose of &quot;let expression&quot; (LetExpr) in the Java compiler?

The Java compiler seems to have support for <code>let</code> expressions in <code>com.sun.tools.javac.tree.*</code> (look for <code>LetExpr</code>).
One comment in JCTree even mentions some syntax
<pre><code class="hljs language-ini">(let int x = 3; in x+2)
</code></pre>
which of course is not accepted by the grammar of the language and rejected in an earlier compiler phase.
I'm wondering about the origin of this construct, which I have never seen before.
Is it used internally by <code>javac</code> or is it synthesized by other tools? Is it maybe just an artifact from the very early days of Java from a language feature which never saw the light?
Is there anything useful which can be done with it today?
Generally speaking, why does it exist?

 I&#39;ve been following the getting started tutorial, but am stuck after I imported the playn project using Maven.  I am using Eclipse Indigo running on 64bit Windows 7.

  All the imported projects have the same error:

    Missing Artifact com.sun:tools:jar in all the pom.xml files.

After a couple hours of searching forums I have tried:

Installing the latest Java 1.6.029
Changing my `JAVA_HOME` environment variable to point to `\program files\Java\jdk1.6_029`
Changing my Eclipse Java preferences to use the JRE `jdk1.6_029`.

 I would really like to experiment with playn, but why there are a few posts I can&#39;t seem to find a consenus answer on the solution.   Some people say Sun removed something from the 64bit jdk, others say you must edit your xml files, many people have said you have change your `JAVA_HOME`, and another said you have to change your VM options for Eclipse.

  Any help on clearing this up would be appreciated, and possibly useful for many, since I do not have a particularly odd setup here.

(edit)
Here is the pom.xml in the first project.  Eclipse flags error in the line which says:

&lt;!-- language: lang-xml --&gt;

    &lt;project xmlns=&quot;http://maven.apache.org/POM/4.0.0&quot; xmlns:xsi=&quot;http://www.w3.org/2001/XMLSchema-instance&quot; xsi:schemaLocation=&quot;http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd&quot;&gt;
      &lt;modelVersion&gt;4.0.0&lt;/modelVersion&gt;
    
      &lt;parent&gt;
        &lt;groupId&gt;com.googlecode.playn&lt;/groupId&gt;
        &lt;artifactId&gt;playn-project&lt;/artifactId&gt;
        &lt;version&gt;1.1-SNAPSHOT&lt;/version&gt;
      &lt;/parent&gt;
    
      &lt;artifactId&gt;playn-android&lt;/artifactId&gt;
      &lt;name&gt;PlayN Android&lt;/name&gt;
      &lt;packaging&gt;jar&lt;/packaging&gt;
    
      &lt;repositories&gt;
      &lt;/repositories&gt;
    
      &lt;dependencies&gt;
        &lt;dependency&gt;
          &lt;groupId&gt;com.googlecode.playn&lt;/groupId&gt;
          &lt;artifactId&gt;playn-core&lt;/artifactId&gt;
          &lt;version&gt;${project.version}&lt;/version&gt;
        &lt;/dependency&gt;
    
        &lt;!-- needed because Android uses the same JSON code as playn-java;
             that should be factored into a library shared by both backends --&gt;
        &lt;dependency&gt;
          &lt;groupId&gt;com.googlecode.playn&lt;/groupId&gt;
          &lt;artifactId&gt;playn-java&lt;/artifactId&gt;
          &lt;version&gt;${project.version}&lt;/version&gt;
        &lt;/dependency&gt;
    
        &lt;dependency&gt;
          &lt;groupId&gt;com.google.android&lt;/groupId&gt;
          &lt;artifactId&gt;android&lt;/artifactId&gt;
          &lt;version&gt;${android.version}&lt;/version&gt;
          &lt;scope&gt;provided&lt;/scope&gt;
        &lt;/dependency&gt;
    
        &lt;dependency&gt;
          &lt;groupId&gt;junit&lt;/groupId&gt;
          &lt;artifactId&gt;junit&lt;/artifactId&gt;
          &lt;version&gt;4.8.1&lt;/version&gt;
          &lt;scope&gt;test&lt;/scope&gt;
        &lt;/dependency&gt;
      &lt;/dependencies&gt;
    
      &lt;build&gt;
        &lt;sourceDirectory&gt;src&lt;/sourceDirectory&gt;
      &lt;/build&gt;
    &lt;/project&gt;


Missing artifact com.sun:tools:jar

I am switching from Java to C++ and I was wondering whether C++ contains the enhanced for loops that I used in java, in example:

    int[] numbers = {1,2,3,4,5,6,7,8,9,10};
    for (int item : numbers) {
      System.out.println(&quot;Count is: &quot; + item);
    }
Is this same &quot;shortcut&quot; possible in C++?

Enhanced FOR loops in C++

I&#39;ve done some research, and I seem to be missing one small part of this algorithm. I understand how a Breadth-First Search works, but I don&#39;t understand how exactly it will get me to a specific path, as opposed to just telling me where each individual node can go. I guess the easiest way to explain my confusion is to provide an example:

So for instance, let&#39;s say I have a graph like this:

![enter image description here][1]

And my goal is to get from A to E (all edges are unweighted).

I start at A, because that&#39;s my origin. I queue A, followed by immediately dequeueing A and exploring it. This yields B and D, because A is connected to B and D. I thus queue both B and D.

I dequeue B and explore it, and find that it leads to A (already explored), and C, so I queue C. I then dequeue D, and find that it leads to E, my goal. I then dequeue C, and find that it also leads to E, my goal.

I know logically that the fastest path is A-&gt;D-&gt;E, but I&#39;m not sure how exactly the breadth-first search helps - how should I be recording paths such that when I finish, I can analyze the results and see that the shortest path is A-&gt;D-&gt;E?

Also, note that I&#39;m not actually using a tree, so there are no &quot;parent&quot; nodes, only children.


  [1]: http://i.stack.imgur.com/e9PxE.jpg

How does a Breadth-First Search work when looking for Shortest Path?

I want to put a Listener over a `CheckBox`. I looked for info and it is like this:

    satView = (CheckBox)findViewById(R.id.sateliteCheckBox);
    
    satView.setOnCheckedChangeListener(new OnCheckedChangeListener() {
		@Override
		public void onCheckedChanged(RadioGroup group, int checkedId) {
            if (isChecked){
                // perform logic
            }
		}

    });

The problem is that Eclipse thinks it&#39;s an `OnCheckedChangeListener` for a `RadioGroup` and it doesn&#39;t work. How can I fix this?

Android: checkbox listener

For example:
    
    class A {
        static int i=0;
        static int j;

       static void method() {
           // static k=0; can&#39;t use static for local variables only final is permitted
           // static int L;
        }
    }

Where will these variables be stored in Java, in heap or in stack memory? How are they stored?

Where are static methods and static variables stored in Java?

Is there any way or tool to apply GPU acceleration on compiling programs with GCC compiler? Right now I have created a program to compile the given list of programs iteratively. It takes a few minutes. I know of a few programs like Pyrit which helps to apply GPU acceleration for precomputing hashes.

If there are no such tools available, Please advice on whether to use OpenCL or anything else to reprogram my code.

Is it possible to use GPU acceleration on compiling multiple programs on a gcc compiler?

I&#39;ve always been a little confused about what&#39;s going on here:

    #include &lt;stdio.h&gt;

    int main() {  
        timeval tv;
        tv.tv_sec = 1;

        for (;;) {
            select(0, 0, 0, 0, &amp;tv);
            printf(&quot;%s\n&quot;, &quot;Hello World!&quot;);
        }
    }

Sorry if that doesn&#39;t compile, just wrote it as a quick example.

Code like this won&#39;t compile under gcc unless I add the keyword **struct** prior to the use of the struct timeval.  g++ on the other hand handles it fine as is.

Is this a difference between how C and C++ handle structures or is it just a difference in the compilers?  (I&#39;m very C++ oriented, and the use of struct in C on lines like this has always somewhat baffled me).



Why does C need &quot;struct&quot; keyword and not C++?

What would be the easiest way to create a C compiler for a custom CPU, assuming of course I already have an assembler for it?

Since a C compiler generates assembly, is there some way to just define standard bits and pieces of assembly code for the various C idioms, rebuild the compiler, and thereby obtain a cross compiler for the target hardware?

Preferably the compiler itself would be written in C, and build as a native executable for either Linux or Windows.


**Please note:** I am _not_ asking how to write the compiler itself. I did take that course in college, I know about general compiler-compilers, etc. In this situation, I&#39;d just like to configure some existing framework if at all possible. I don&#39;t want to modify the language, I just want to be able to target an arbitrary architecture. If the answer turns out to be &quot;it doesn&#39;t work that way&quot;, *that* information will be useful to myself and anyone else who might make similar assumptions.

How to create a C compiler for custom CPU?

What flag(s) do I need on the command line to disable the return-value optimisation automatically enabled by the g++ compiler?

Disabling g++&#39;s return-value optimisation

In a recent interview, I was asked a really strange question. The interviewer asked me how can I compute 1+2+3+...+1000 just using compiler features. This means that I am not allowed to write a program and execute it, but I should just write a program that could drive the compiler to compute this sum while compilation and print the result when compilation completes. As a hint, he told me that I may use generics and pre-processor features of the compiler. It is possible to use C++, C# or Java compiler. Any ideas???

This question is not related to computing the sum without any loops [asked here][1]. In addition, It should be noted that the sum SHOULD be calculated during compilation. Printing just the result using C++ compiler directives is not acceptable. 

&lt;hr&gt;

Reading more about the posted answers, I found that solving problems during compilation using C++ templates is called **metaprogramming**. This is a technique that was discovered accidentally by Dr. Erwin Unruh,  during the process of standardizing the C++ language. You may read more about this topic on [wiki page of meta-programming][2].
It seems that it is possible to write the program in Java using java annotations. You may take a look at **[maress&#39;s][3]** answer below. 

A nice book about meta-programming in C++ is [this one][4]. Worth to take a look if interested. 

A useful C++ meta-programming library is Boost&#39;s MPL [this link][5].


  [1]: https://stackoverflow.com/questions/4568645/printing-1-to-1000-without-loop-or-conditionals/4568650#4568650
  [2]: http://en.wikipedia.org/wiki/Template_metaprogramming
  [3]: https://stackoverflow.com/a/8815298/114029
  [4]: http://www.amazon.com/Modern-Design-Generic-Programming-Patterns/dp/0201704315
  [5]: http://www.boost.org/doc/libs/1_58_0/libs/mpl/doc/index.html

How to drive C#, C++ or Java compiler to compute 1+2+3+...+1000 at compile time?

Today, while I was randomly reading the JavaScript patterns O&#39;Reilly book, I found one interesting thing (page 27 for reference).

In Javascript, in some cases, there is a difference if the brace start location is different.

    function test_function1() {
        return
        {
            name: &#39;rajat&#39;
        };
    }

    var obj = test_function1();
    alert(obj);  //Shows &quot;undefined&quot;

While  

    function test_function2() {
        return {
            name: &#39;rajat&#39;
        };
    }

    var obj = test_function2();
    alert(obj); //Shows object

[JSfiddle Demo][1]

Does any other language out there have such behavior? If so, then I would have to change my habit for sure..:)

I am mainly concerned about PHP, C, C++, Java, and ruby.

  [1]: http://jsfiddle.net/PmaNp/


Does any other language other than JavaScript have a difference between brace start locations (same line and next line)?

Is there any rule about which built-in and standard library classes are not subclassable (&quot;final&quot;)?

As of Python 3.3, here are a few examples:

  - `bool`
  - `function`
  - `operator.itemgetter`
  - `slice`

I found a [question][1] which deals with the implementation of &quot;final&quot; classes, both in C and pure Python.

I would like to understand what reasons may explain why a class is chosen to be &quot;final&quot; in the first place. 


  [1]: https://stackoverflow.com/questions/2825364/final-classes-in-python-3-x-something-guido-isnt-telling-me

Which classes cannot be subclassed?

I was coding today and noticed something. If I open a new interpreter session (IDLE) and check what&#39;s defined with the `dir` function I get this:

    $ python
    &gt;&gt;&gt; dir()
    [&#39;__builtins__&#39;, &#39;__doc__&#39;, &#39;__name__&#39;, &#39;__package__&#39;]
    &gt;&gt;&gt; dir(__builtins__)
    [&#39;ArithmeticError&#39;, &#39;AssertionError&#39;, &#39;AttributeError&#39;, &#39;BaseException&#39;, &#39;BufferError&#39;, &#39;BytesWarning&#39;, &#39;DeprecationWarning&#39;, &#39;EOFError&#39;, &#39;Ellipsis&#39;, &#39;EnvironmentError&#39;, &#39;Exception&#39;, &#39;False&#39;, &#39;FloatingPointError&#39;, &#39;FutureWarning&#39;, &#39;GeneratorExit&#39;, &#39;IOError&#39;, &#39;ImportError&#39;, &#39;ImportWarning&#39;, &#39;IndentationError&#39;, &#39;IndexError&#39;, &#39;KeyError&#39;, &#39;KeyboardInterrupt&#39;, &#39;LookupError&#39;, &#39;MemoryError&#39;, &#39;NameError&#39;, &#39;None&#39;, &#39;NotImplemented&#39;, &#39;NotImplementedError&#39;, &#39;OSError&#39;, &#39;OverflowError&#39;, &#39;PendingDeprecationWarning&#39;, &#39;ReferenceError&#39;, &#39;RuntimeError&#39;, &#39;RuntimeWarning&#39;, &#39;StandardError&#39;, &#39;StopIteration&#39;, &#39;SyntaxError&#39;, &#39;SyntaxWarning&#39;, &#39;SystemError&#39;, &#39;SystemExit&#39;, &#39;TabError&#39;, &#39;True&#39;, &#39;TypeError&#39;, &#39;UnboundLocalError&#39;, &#39;UnicodeDecodeError&#39;, &#39;UnicodeEncodeError&#39;, &#39;UnicodeError&#39;, &#39;UnicodeTranslateError&#39;, &#39;UnicodeWarning&#39;, &#39;UserWarning&#39;, &#39;ValueError&#39;, &#39;Warning&#39;, &#39;ZeroDivisionError&#39;, &#39;_&#39;, &#39;__debug__&#39;, &#39;__doc__&#39;, &#39;__import__&#39;, &#39;__name__&#39;, &#39;__package__&#39;, &#39;abs&#39;, &#39;all&#39;, &#39;any&#39;, &#39;apply&#39;, &#39;basestring&#39;, &#39;bin&#39;, &#39;bool&#39;, &#39;buffer&#39;, &#39;bytearray&#39;, &#39;bytes&#39;, &#39;callable&#39;, &#39;chr&#39;, &#39;classmethod&#39;, &#39;cmp&#39;, &#39;coerce&#39;, &#39;compile&#39;, &#39;complex&#39;, &#39;copyright&#39;, &#39;credits&#39;, &#39;delattr&#39;, &#39;dict&#39;, &#39;dir&#39;, &#39;divmod&#39;, &#39;enumerate&#39;, &#39;eval&#39;, &#39;execfile&#39;, &#39;exit&#39;, &#39;file&#39;, &#39;filter&#39;, &#39;float&#39;, &#39;format&#39;, &#39;frozenset&#39;, &#39;getattr&#39;, &#39;globals&#39;, &#39;hasattr&#39;, &#39;hash&#39;, &#39;help&#39;, &#39;hex&#39;, &#39;id&#39;, &#39;input&#39;, &#39;int&#39;, &#39;intern&#39;, &#39;isinstance&#39;, &#39;issubclass&#39;, &#39;iter&#39;, &#39;len&#39;, &#39;license&#39;, &#39;list&#39;, &#39;locals&#39;, &#39;long&#39;, &#39;map&#39;, &#39;max&#39;, &#39;memoryview&#39;, &#39;min&#39;, &#39;next&#39;, &#39;object&#39;, &#39;oct&#39;, &#39;open&#39;, &#39;ord&#39;, &#39;pow&#39;, &#39;print&#39;, &#39;property&#39;, &#39;quit&#39;, &#39;range&#39;, &#39;raw_input&#39;, &#39;reduce&#39;, &#39;reload&#39;, &#39;repr&#39;, &#39;reversed&#39;, &#39;round&#39;, &#39;set&#39;, &#39;setattr&#39;, &#39;slice&#39;, &#39;sorted&#39;, &#39;staticmethod&#39;, &#39;str&#39;, &#39;sum&#39;, &#39;super&#39;, &#39;tuple&#39;, &#39;type&#39;, &#39;unichr&#39;, &#39;unicode&#39;, &#39;vars&#39;, &#39;xrange&#39;, &#39;zip&#39;]
    &gt;&gt;&gt; import __builtin__
    [&#39;ArithmeticError&#39;, &#39;AssertionError&#39;, &#39;AttributeError&#39;, &#39;BaseException&#39;, &#39;BufferError&#39;, &#39;BytesWarning&#39;, &#39;DeprecationWarning&#39;, &#39;EOFError&#39;, &#39;Ellipsis&#39;, &#39;EnvironmentError&#39;, &#39;Exception&#39;, &#39;False&#39;, &#39;FloatingPointError&#39;, &#39;FutureWarning&#39;, &#39;GeneratorExit&#39;, &#39;IOError&#39;, &#39;ImportError&#39;, &#39;ImportWarning&#39;, &#39;IndentationError&#39;, &#39;IndexError&#39;, &#39;KeyError&#39;, &#39;KeyboardInterrupt&#39;, &#39;LookupError&#39;, &#39;MemoryError&#39;, &#39;NameError&#39;, &#39;None&#39;, &#39;NotImplemented&#39;, &#39;NotImplementedError&#39;, &#39;OSError&#39;, &#39;OverflowError&#39;, &#39;PendingDeprecationWarning&#39;, &#39;ReferenceError&#39;, &#39;RuntimeError&#39;, &#39;RuntimeWarning&#39;, &#39;StandardError&#39;, &#39;StopIteration&#39;, &#39;SyntaxError&#39;, &#39;SyntaxWarning&#39;, &#39;SystemError&#39;, &#39;SystemExit&#39;, &#39;TabError&#39;, &#39;True&#39;, &#39;TypeError&#39;, &#39;UnboundLocalError&#39;, &#39;UnicodeDecodeError&#39;, &#39;UnicodeEncodeError&#39;, &#39;UnicodeError&#39;, &#39;UnicodeTranslateError&#39;, &#39;UnicodeWarning&#39;, &#39;UserWarning&#39;, &#39;ValueError&#39;, &#39;Warning&#39;, &#39;ZeroDivisionError&#39;, &#39;_&#39;, &#39;__debug__&#39;, &#39;__doc__&#39;, &#39;__import__&#39;, &#39;__name__&#39;, &#39;__package__&#39;, &#39;abs&#39;, &#39;all&#39;, &#39;any&#39;, &#39;apply&#39;, &#39;basestring&#39;, &#39;bin&#39;, &#39;bool&#39;, &#39;buffer&#39;, &#39;bytearray&#39;, &#39;bytes&#39;, &#39;callable&#39;, &#39;chr&#39;, &#39;classmethod&#39;, &#39;cmp&#39;, &#39;coerce&#39;, &#39;compile&#39;, &#39;complex&#39;, &#39;copyright&#39;, &#39;credits&#39;, &#39;delattr&#39;, &#39;dict&#39;, &#39;dir&#39;, &#39;divmod&#39;, &#39;enumerate&#39;, &#39;eval&#39;, &#39;execfile&#39;, &#39;exit&#39;, &#39;file&#39;, &#39;filter&#39;, &#39;float&#39;, &#39;format&#39;, &#39;frozenset&#39;, &#39;getattr&#39;, &#39;globals&#39;, &#39;hasattr&#39;, &#39;hash&#39;, &#39;help&#39;, &#39;hex&#39;, &#39;id&#39;, &#39;input&#39;, &#39;int&#39;, &#39;intern&#39;, &#39;isinstance&#39;, &#39;issubclass&#39;, &#39;iter&#39;, &#39;len&#39;, &#39;license&#39;, &#39;list&#39;, &#39;locals&#39;, &#39;long&#39;, &#39;map&#39;, &#39;max&#39;, &#39;memoryview&#39;, &#39;min&#39;, &#39;next&#39;, &#39;object&#39;, &#39;oct&#39;, &#39;open&#39;, &#39;ord&#39;, &#39;pow&#39;, &#39;print&#39;, &#39;property&#39;, &#39;quit&#39;, &#39;range&#39;, &#39;raw_input&#39;, &#39;reduce&#39;, &#39;reload&#39;, &#39;repr&#39;, &#39;reversed&#39;, &#39;round&#39;, &#39;set&#39;, &#39;setattr&#39;, &#39;slice&#39;, &#39;sorted&#39;, &#39;staticmethod&#39;, &#39;str&#39;, &#39;sum&#39;, &#39;super&#39;, &#39;tuple&#39;, &#39;type&#39;, &#39;unichr&#39;, &#39;unicode&#39;, &#39;vars&#39;, &#39;xrange&#39;, &#39;zip&#39;]
    &gt;&gt;&gt; dir(__builtin__) == dir(__builtins__) # They seem to have the same things
    True

Please note the last line.

So, my question is:

 - Is any an alias of the other one?
   
 - Are the Python guys planning to get rid of one of those?
   
 - What should I use for my own programs?

 - What about Python 3?

 - Any information is valuable!

**Important:**

I&#39;m using Python 2.7.2+  on Ubuntu.

What&#39;s the difference between __builtin__ and __builtins__?

&gt; **Possible Duplicate:**  
&gt; [Why is Java&amp;#39;s Iterator not an Iterable?](https://stackoverflow.com/questions/839178/why-is-javas-iterator-not-an-iterable)  
&gt;
&gt; https://stackoverflow.com/questions/3883131/idiomatic-way-to-use-for-each-loop-given-an-iterator
&gt;
&gt; https://stackoverflow.com/questions/2162917/can-we-use-for-each-loop-for-iterating-the-objects-of-iterator-type

&lt;!-- End of automatically inserted text --&gt;

The foreach loop are as far as I know syntax sugar added in Java 5. So

    Iterable&lt;O&gt; iterable;
    for(O o : iterable) {
        // Do something
    }

will essentially produce the same bytecode as

    Iterable&lt;O&gt; iterable;
    for(Iterator&lt;O&gt; iter = iterable.iterator(); iter.hasNext(); /* NOOP */) {
        O o = iter.next();
        // Do something
    }

However, if I do not have an iterable in the first place, but only an iterator (say, because a class offers two different iterators), I cannot use the syntax sugar foreach loop. Obviously I can still do the plain old style iteration. However, I&#39;d actually like to do:

    Iterator&lt;O&gt; iter;
    for(O o : iter /* Iterator&lt;O&gt;, not Iterable&lt;O&gt;! */) {
         // Do something
    }

And of course I can do a fake `Iterable`:

    class Adapter&lt;O&gt; implements Iterable&lt;O&gt; {
        Iterator&lt;O&gt; iter;

        public Adapter(Iterator&lt;O&gt; iter) {
            this.iter = iter;
        }

        @Override
        public Iterator&lt;O&gt; iterator() {
            return iter;
        }
    }

(Which in fact is an ugly abuse of the Iterable API, as it can only be iterated once!)

If it were designed around `Iterator` instead of iterable, one could do a number of interesting things:

    for(O o : iterable.iterator()) {} // Iterate over Iterable and Collections

    for(O o : list.backwardsIterator()) {} // Or backwards

    Iterator&lt;O&gt; iter;
    for(O o : iter) {
        if (o.something()) { iter.remove(); }
        if (o.something()) { break; }
    }
    for(O : iter) { } // Do something with the remaining elements only.

Does anyone know *why* the language was designed this way? To avoid ambiguity if a class would implement both `Iterator` and `Iterable`? To avoid programmer errors that assume that &quot;for(O o : iter)&quot; will process all elements twice (and forget to get a fresh iterator)? Or is there some other reason for this?

Or is there some language trick I just do not know?

Why does Java not allow foreach on iterators (only on iterables)?

Disclaimer: I am not asking _if_ the upper-bound `stop`argument of `slice()`and `range()` is exclusive or _how_ to use these functions.

Calls to the `range`and `slice`functions, as well as the slice notation `[start:stop]` all refer to sets of integers.

    range([start], stop[, step])
    slice([start], stop[, step])
In all these, the `stop` integer is excluded.

**I am wondering _why_ the language is designed this way.**


Is it to make `stop`equal to the number of elements in the represented integer set when `start` equals 0 or is omitted?

Is it to have:

    for i in range(start, stop):
look like the following C code?

    for (i = start ; i &lt; stop; i++) {


Why are slice and range upper-bound exclusive?

I want to use Lazy initialization for some of my properties in Swift.
My current code looks like this:


    lazy var fontSize : CGFloat = {
      if (someCase) {
        return CGFloat(30)
      } else {
        return CGFloat(17)
      }
    }()

The thing is that once the fontSize is set it will NEVER change.
So I wanted to do something like this:

    lazy let fontSize : CGFloat = {
      if (someCase) {
        return CGFloat(30)
      } else {
        return CGFloat(17)
      }
    }()

Which is impossible.

Only this works:

    let fontSize : CGFloat = {
      if (someCase) {
        return CGFloat(30)
      } else {
        return CGFloat(17)
      }
    }()

So - I want a property that will be lazy loaded but will never change.
What is the correct way to do that? using `let` and forget about the lazy init? Or should I use `lazy var` and forget about the constant nature of the property?

Lazy Var vs Let

In JavaScript, `var` declarations create properties on the global object:

    var x = 15;
    console.log(window.x); // logs 15 in browser
    console.log(global.x); // logs 15 in Node.js

ES6 introduces lexical scoping with [`let`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/let) declarations that have block scope.

    let x = 15;
    {
       let x = 14;
    }
    console.log(x); // logs 15;

However, do these declarations create properties on the global object?

    let x = 15;
    // what is this supposed to log in the browser according to ES6?
    console.log(window.x); // 15 in Firefox
    console.log(global.x); // undefined in Node.js with flag

Do let statements create properties on the global object?

I have been playing with ES6 for a while and I noticed that while variables declared with `var` are hoisted as expected...

    console.log(typeof name); // undefined
    var name = &quot;John&quot;;


...variables declared with `let` or `const` seem to have some problems with hoisting:

    console.log(typeof name); // ReferenceError
    let name = &quot;John&quot;;

and

    console.log(typeof name); // ReferenceError
    const name = &quot;John&quot;;

Does this mean that variables declared with `let` or `const` are not hoisted? What is really going on here? Is there any difference between `let` and `const` in this matter?

Are variables declared with let or const hoisted?

This code logs `6`, 6 times:

    (function timer() {
      for (var i=0; i&lt;=5; i++) {
        setTimeout(function clog() {console.log(i)}, i*1000);
      }
    })();

But this code...

    (function timer() {
      for (let i=0; i&lt;=5; i++) {
        setTimeout(function clog() {console.log(i)}, i*1000);
      }
    })();

... logs the following result:

    0
    1
    2
    3
    4
    5

Why?

Is it because `let` binds to the inner scope each item differently and `var` keeps the latest value of `i`?

Why let and var bindings behave differently using setTimeout function?

I&#39;ve heard that accessing `let` and `const` values before they are initialized can cause a `ReferenceError` because of something called the **temporal dead zone**.

What is the temporal dead zone, how does it relate to scope and hoisting, and in what situations is it encountered?



Content Type	Original Author	Original Content on Stackoverflow
Question	soc	View Question on Stackoverflow
Solution 1 - Java	Armin Ronacher	View Answer on Stackoverflow
Solution 2 - Java	Danny Milosavljevic	View Answer on Stackoverflow

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