In Perl (and other languages) a conditional ternary operator can be expressed like this:

    my $foo = $bar == $buz ? $cat : $dog;

Is there a similar operator in VB.NET?


Is there a conditional ternary operator in VB.NET?

Does Python support short-circuiting in boolean expressions?

Does Python support short-circuiting?

What construct should I use to check whether a value is NULL in a Twig template?

How to check for null in Twig?

In VB.NET, what is the difference between `And` and `AndAlso`? Which should I use?


What is the difference between And and AndAlso in VB.NET?

Does the ANSI standard *mandate* the logical operators to be short-circuited, in either C or C++?

I&#39;m confused for I recall the K&amp;R book saying your code shouldn&#39;t depend on these operations being short circuited, for they may not. Could someone please point out where in the standard it&#39;s said logic ops are always short-circuited? I&#39;m mostly interested on C++, an answer also for C would be great.

I also remember reading (can&#39;t remember where) that evaluation order isn&#39;t strictly defined, so your code shouldn&#39;t depend or assume functions within an expression would be executed in a specific order: by the end of a statement all referenced functions will have been called, but the compiler has freedom in selecting the most efficient order.

Does the standard indicate the evaluation order of this expression?

    if( functionA() &amp;&amp; functionB() &amp;&amp; functionC() ) cout&lt;&lt;&quot;Hello world&quot;;

Is short-circuiting logical operators mandated? And evaluation order?

Are boolean expressions in SQL WHERE clauses [short-circuit evaluated
](http://en.wikipedia.org/wiki/Short-circuit_evaluation)? 

For example:

    SELECT * 
    FROM Table t 
    WHERE @key IS NULL OR (@key IS NOT NULL AND @key = t.Key) 

If `@key IS NULL` evaluates to `true`, is `@key IS NOT NULL AND @key = t.Key` evaluated?

If no, why not?

If yes, is it guaranteed? Is it part of ANSI SQL or is it database specific?

If database specific, SQLServer? Oracle? MySQL?

Is the SQL WHERE clause short-circuit evaluated?

The short circuiting behaviour of the operators `&amp;&amp;` and `||` is an amazing tool for programmers.

But why do they lose this behaviour when overloaded? I understand that operators are merely syntactic sugar for functions but the operators for `bool` have this behaviour, why should it be restricted to this single type? Is there any technical reasoning behind this?

Is there actually a reason why overloaded &amp;&amp; and || don&#39;t short circuit?

I would like to know if JavaScript has &quot;short-circuit&quot; evaluation like &amp;&amp; Operator in C#. If not, I would like to know if there is a workaround that makes sense to adopt.
 

Does JavaScript have &quot;Short-circuit&quot; evaluation?

I have the following simple short-circuit statement that should show either a component or nothing:

`{profileTypesLoading &amp;&amp; &lt;GeneralLoader /&gt;}`

If the statement is false, it renders a `0` instead of nothing.

I have done a `console.log(profileTypesLoading)` just to see quickly what the status of the `profileTypesLoading` property is and it&#39;s either 1 or 0 as expected.  0 should be false... causing nothing to render.  Right?

Any idea why this would happen?

React showing 0 instead of nothing with short-circuit (&amp;&amp;) conditional component

Preparing for the Oracle Certified Associate Java SE 8 Programmer 1 exam, I came across the following paragraph about the ternary expression in the official Study Guide:

&gt;**Ternary Expression Evaluation**
&gt;&lt;br/&gt;
&gt;As of Java 7, only one of the right-hand expressions of the ternary operator will be evaluated at runtime. In a manner similar to the short-circuit operators, if one of the two right-hand expressions in a ternary operator performs a side effect, then it may not be applied at runtime. Let&#39;s illustrate this principle with the following example: [...]

It says that only one of the two expressions is evaluated, demonstrating with the following example:

    int y = 1;
    int z = 1;
    int a = y &lt; 10 ? y++ : z++;

Here, only `y` increments, but `z` does not, as you would expect.

What I am stumbling across is the beginning of the paragraph (marked in yellow) where it says &quot;As of Java 7, ...&quot;. I tested the same code with Java 1.6 and I can&#39;t find a difference in the behavior. I expected Java 1.6 to evaluate both expressions just from the information given in the paragraph. Does anyone have an idea what they wanted to say with &quot;As of Java 7,  ...&quot;?

**Edit:** To avoid confusion: It boils down to the question, Since they write &#39;As of Java 7&#39;, was there anything that changed concerning the ternary operator, when switching from Java 6 to Java 7?


  [1]: http://i.stack.imgur.com/PaazW.jpg

Ternary operator in Java only evaluating one expression since Java 7 - was that different in Java 1.6 and lower?

What is the difference between the `&amp;` and `&amp;&amp;` logical operators in MATLAB?

What&#39;s the difference between &amp; and &amp;&amp; in MATLAB?

In PHP we can check if a key exists in an array by using the function `array_key_exists()`.

In the Twig templating language we can check if an variable or an object&#39;s property exists simply by using an `if` statement, like this:

    {% if app.user %}
    do something here
    {% else %}
    do something else
    {% endif %}

But how do we check if a key of an *array* exists using Twig? I tried `{% if array.key %}`, but it gives me an error:

    Key &quot;key&quot; for array with keys &quot;0, 1, 2, 3...648&quot; does not exist

As one of the primary ways of passing data into a template is using arrays, it seems like there should be some way of doing this. Any thoughts?

In Twig, check if a specific key of an array exists

Sometimes, an `if` statement can be rather complicated or long, so for the sake of readability it is better to extract complicated calls before the `if`.

 e.g. this:

    if (SomeComplicatedFunctionCall() || OtherComplicatedFunctionCall())
	{
		// do stuff
	}

into this

	bool b1 = SomeComplicatedFunctionCall();
	bool b2 = OtherComplicatedFunctionCall();

	if (b1 || b2)
	{
		//do stuff
	}


(provided example is not _that_ bad, it&#39;s just for illustration... imagine other calls with multiple arguments, etc.)

But with this extraction I lost the short circuit evaluation (SCE).

1. Do I really lose SCE every time? Is there some scenario where the compiler is allowed to &quot;optimize it&quot; and still provide SCE?
2. Are there ways of keeping the improved readability of the second snippet without losing SCE?

if statement - short circuit evaluation vs readability

So for binary operators on booleans, Java has `&amp;`, `|`, `^`, `&amp;&amp;` and `||`.

Let&#39;s summarize what they do briefly here:

 * &lt;a href=&quot;http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.22.2&quot;&gt;JLS 15.22.2 Boolean Logical Operators &amp;, ^, and |&lt;/a&gt;
 * &lt;a href=&quot;http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.23&quot;&gt;JLS 15.23 Conditional-And Operator &amp;&amp;&lt;/a&gt; 
 * &lt;a href=&quot;http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.24&quot;&gt;JLS 15.24 Conditional-Or Operator ||&lt;/a&gt;

&gt; For `&amp;`, the result value is `true` if both operand values are `true`; otherwise, the result is `false`.
&gt;
&gt; For `|`, the result value is `false` if both operand values are `false`; otherwise, the result is `true`.
&gt;
&gt; For `^`, the result value is `true` if the operand values are different; otherwise, the result is `false`.
&gt;
&gt; The `&amp;&amp;` operator is like `&amp;` but evaluates its right-hand operand only if the value of its left-hand operand is `true`.
&gt;
&gt; The `||` operator is like `|`, but evaluates its right-hand operand only if the value of its left-hand operand is `false`.

Now, among all 5, 3 of those have compound assignment versions, namely `|=`, `&amp;=` and `^=`. So my question is obvious: why doesn&#39;t Java provide `&amp;&amp;=` and `||=` as well? I find that I need those more than I need `&amp;=` and `|=`.

And I don&#39;t think that &quot;because it&#39;s too long&quot; is a good answer, because Java has `&gt;&gt;&gt;=`. There must be a better reason for this omission.

----

From &lt;a href=&quot;http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.26&quot;&gt;15.26 Assignment Operators&lt;/a&gt;:

&gt; There are 12 assignment operators; [...] `= *= /= %= += -= &lt;&lt;= &gt;&gt;= &gt;&gt;&gt;= &amp;= ^= |=`

----

A comment was made that if `&amp;&amp;=` and `||=` were implemented, then it would be the only operators that do not evaluate the right hand side first. I believe this notion that a compound assignment operator evaluates the right hand side first is a mistake.

From &lt;a href=&quot;http://java.sun.com/docs/books/jls/third_edition/html/expressions.html#15.26.2&quot;&gt;15.26.2 Compound Assignment Operators&lt;/a&gt;:

&gt; A compound assignment expression of the form `E1 op= E2` is equivalent to `E1 = (T)((E1) op (E2))`, where `T` is the type of `E1`, except that `E1` is evaluated only once. 
&gt; 

As proof, the following snippet throws a `NullPointerException`, not an `ArrayIndexOutOfBoundsException`.

		int[] a = null;
		int[] b = {};
		a[0] += b[-1];



Why doesn&#39;t Java have compound assignment versions of the conditional-and and conditional-or operators? (&amp;&amp;=, ||=)

I read the C# Language Specification on the _Conditional logical operators_ `||` and `&amp;&amp;`, also known as the short-circuiting logical operators. To me it seemed unclear if these existed for nullable booleans, i.e. the operand type `Nullable&lt;bool&gt;` (also written `bool?`), so I tried it with non-dynamic typing:

    bool a = true;
    bool? b = null;
    bool? xxxx = b || a;  // compile-time error, || can&#39;t be applied to these types

That seemed to settle the question (I could not understand the specification clearly, but assuming the implementation of the Visual C# compiler was correct, now I knew).

However, I wanted to try with `dynamic` binding as well. So I tried this instead:

    static class Program
    {
      static dynamic A
      {
        get
        {
          Console.WriteLine(&quot;&#39;A&#39; evaluated&quot;);
          return true;
        }
      }
      static dynamic B
      {
        get
        {
          Console.WriteLine(&quot;&#39;B&#39; evaluated&quot;);
          return null;
        }
      }
    
      static void Main()
      {
        dynamic x = A | B;
        Console.WriteLine((object)x);
        dynamic y = A &amp; B;
        Console.WriteLine((object)y);

        dynamic xx = A || B;
        Console.WriteLine((object)xx);
        dynamic yy = A &amp;&amp; B;
        Console.WriteLine((object)yy);
      }
    }

The surprising result is that this runs without exception.

Well, `x` and `y` are not surprising, their declarations lead to both properties being retrieved, and the resulting values are as expected, `x` is `true` and `y` is `null`.

But the evaluation for `xx` of `A || B` lead to no binding-time exception, and only the property `A` was read, not `B`. Why does this happen? As you can tell, we could change the `B` getter to return a crazy object, like `&quot;Hello world&quot;`, and `xx` would still evaluate to `true` without binding-problems...

Evaluating `A &amp;&amp; B` (for `yy`) also leads to no binding-time error. And here both properties are retrieved, of course. Why is this allowed by the run-time binder? If the returned object from `B` is changed to a &quot;bad&quot; object (like a `string`), a binding exception does occur.

___Is this correct behavior?___ (How can you infer that from the spec?)

If you try `B` as first operand, both `B || A` and `B &amp;&amp; A` give runtime binder exception (`B | A` and `B &amp; A` work fine as everything is normal with non-short-circuiting operators `|` and `&amp;`).

(Tried with C# compiler of Visual Studio 2013, and runtime version .NET 4.5.2.)

Do short-circuiting operators || and &amp;&amp; exist for nullable booleans? The RuntimeBinder sometimes thinks so

Given the following code:

    if (is_valid($string) &amp;&amp; up_to_length($string) &amp;&amp; file_exists($file)) 
    {
        ......
    }

If `is_valid($string)` returns `false`, does the php interpreter still check later conditions, like `up_to_length($string)`?  
If so, then why does it do extra work when it doesn&#39;t have to?

Does PHP have short-circuit evaluation?

Yes, this is a homework question, but I&#39;ve done my research and a fair amount of deep thought on the topic and can&#39;t figure this out. The question states that this piece of code does NOT exhibit [short-circuit behavior][1] and asks why. But it looks to me like it does exhibit short-circuit behavior, so can someone explain why it doesn&#39;t?

In C:

    int sc_and(int a, int b) {
        return a ? b : 0;
    }

It looks to me that in the case that `a` is false, the program will not try to evaluate `b` at all, but I must be wrong. Why does the program even touch `b` in this case, when it doesn&#39;t have to?


  [1]: http://en.wikipedia.org/wiki/Short-circuit_evaluation

Why is this version of logical AND in C not showing short-circuit behavior?

I believe that C# stops evaluating an if statement condition as soon as it is able to tell the outcome. So for example:

    if ( (1 &lt; 0) &amp;&amp; check_something_else() )
        // this will not be called

Since the condition `(1 &lt; 0)` evaluates as `false`, the `&amp;&amp;` condition cannot be met, and `check_something_else()` will not be called.

How does C# evaluate an if statement with asynchronous functions? Does it wait for both to return? So for example:

    if( await first_check() &amp;&amp; await second_check() )
        // ???

Will this ever be short-circuited?

Does C# perform short circuit evaluation of if statements with await?

Assume myObj is null.  Is it safe to write this?  

    if(myObj != null &amp;&amp; myObj.SomeString != null)

I know some languages won&#39;t execute the second expression because the &amp;&amp; evaluates to false before the second part is executed.

Is relying on &amp;&amp; short-circuiting safe in .NET?

When running the following line:

    &gt;&gt;&gt; [0xfor x in (1, 2, 3)]

I expected Python to return an error.

Instead, the REPL returns:

&gt; `[15]`

What can possibly be the reason?

Why does Python return [15] for [0xfor x in (1, 2, 3)]?

When writing code like this in C++:

    bool allTrue = true;
    allTrue = allTrue &amp;&amp; check_foo();
    allTrue = allTrue &amp;&amp; check_bar();

`check_bar()` will not be evaluated if `check_foo()` returned `false`. This is called [short-circuiting or short-circuit evaluation](http://en.wikipedia.org/wiki/Short-circuit_evaluation) and is part of the lazy evaluation principle.

Does this work with the compound assignment operator `&amp;=`?

    bool allTrue = true;
    allTrue &amp;= check_foo();
    allTrue &amp;= check_bar(); //what now?

*For logical `OR` replace all `&amp; ` with `|` and `true` with `false`.*

Do the &amp;= and |= operators for bool short-circuit?

When encountering a (bool1 &amp;&amp; bool2), does c++ ever attempts to check bool2 if bool1 was found false or does it ignore it the way PHP does?

Sorry if it is too basic of a question, but I really could not find a mentioning of that neither in Schildt nor on the Internet.

How does C++ handle &amp;&amp;? (Short-circuit evaluation)

In the [Wikipedia page describing short-circuit evaluation][1], `&amp;` and `|` are listed as eager operators in Python. What does this mean and when are they used in the language? 


  [1]: http://en.wikipedia.org/wiki/Short-circuit_evaluation

Where are the ampersand and vertical bar characters used in Python?

Prompted by the discussion [here](https://stackoverflow.com/a/14721700/174728)

The [docs](http://docs.python.org/2/library/functions.html#all) suggest some equivalent code for the behaviour of [`all`](http://docs.python.org/2/library/functions.html#all) and [`any`](http://docs.python.org/2/library/functions.html#any)

Should the behaviour of the equivalent code be considered part of the definition, or can an implementation implement them in a non-shortcircuit manner?

Here is the relevant excerpt from cpython/Lib/test/test_builtin.py

    def test_all(self):
        self.assertEqual(all([2, 4, 6]), True)
        self.assertEqual(all([2, None, 6]), False)
        self.assertRaises(RuntimeError, all, [2, TestFailingBool(), 6])
        self.assertRaises(RuntimeError, all, TestFailingIter())
        self.assertRaises(TypeError, all, 10)               # Non-iterable
        self.assertRaises(TypeError, all)                   # No args
        self.assertRaises(TypeError, all, [2, 4, 6], [])    # Too many args
        self.assertEqual(all([]), True)                     # Empty iterator
        S = [50, 60]
        self.assertEqual(all(x &gt; 42 for x in S), True)
        S = [50, 40, 60]
        self.assertEqual(all(x &gt; 42 for x in S), False)

    def test_any(self):
        self.assertEqual(any([None, None, None]), False)
        self.assertEqual(any([None, 4, None]), True)
        self.assertRaises(RuntimeError, any, [None, TestFailingBool(), 6])
        self.assertRaises(RuntimeError, all, TestFailingIter())
        self.assertRaises(TypeError, any, 10)               # Non-iterable
        self.assertRaises(TypeError, any)                   # No args
        self.assertRaises(TypeError, any, [2, 4, 6], [])    # Too many args
        self.assertEqual(any([]), False)                    # Empty iterator
        S = [40, 60, 30]
        self.assertEqual(any(x &gt; 42 for x in S), True)
        S = [10, 20, 30]
        self.assertEqual(any(x &gt; 42 for x in S), False)

It doesn&#39;t do anything to enforce the shortcircuit behaviour

All Short Circuiting Solutions on Gang of Coders

Total of 24 Short Circuiting Solutions

Is there a conditional ternary operator in VB.NET?

Does Python support short-circuiting?

How to check for null in Twig?

What is the difference between And and AndAlso in VB.NET?

Is short-circuiting logical operators mandated? And evaluation order?

Is the SQL WHERE clause short-circuit evaluated?

Is there actually a reason why overloaded && and || don't short circuit?

Does JavaScript have "Short-circuit" evaluation?

React showing 0 instead of nothing with short-circuit (&&) conditional component

Ternary operator in Java only evaluating one expression since Java 7 - was that different in Java 1.6 and lower?

What's the difference between & and && in MATLAB?

In Twig, check if a specific key of an array exists

if statement - short circuit evaluation vs readability

Why doesn't Java have compound assignment versions of the conditional-and and conditional-or operators? (&&=, ||=)

Do short-circuiting operators || and && exist for nullable booleans? The RuntimeBinder sometimes thinks so

Does PHP have short-circuit evaluation?

Why is this version of logical AND in C not showing short-circuit behavior?

Does C# perform short circuit evaluation of if statements with await?

Is relying on && short-circuiting safe in .NET?

Why does Python return [15] for [0xfor x in (1, 2, 3)]?

Do the &= and |= operators for bool short-circuit?

How does C++ handle &&? (Short-circuit evaluation)

Where are the ampersand and vertical bar characters used in Python?

Is the shortcircuit behaviour of Python's any/all explicit?