Is there a ternary operator or the like in PHP that acts like `??` of C#?

`??` in C# is clean and shorter, but in PHP you have to do something like:

    // This is absolutely okay except that $_REQUEST[&#39;test&#39;] is kind of redundant.
    echo isset($_REQUEST[&#39;test&#39;])? $_REQUEST[&#39;test&#39;] : &#39;hi&#39;;

    // This is perfect! Shorter and cleaner, but only in this situation.
    echo null? : &#39;replacement if empty&#39;;

    // This line gives error when $_REQUEST[&#39;test&#39;] is NOT set.
    echo $_REQUEST[&#39;test&#39;]?: &#39;hi&#39;;



C#&#39;s null coalescing operator (??) in PHP

Is it possible to do something similar to the following code in Java

    int y = x ?? -1;


[More about `??`][1]


  [1]: https://stackoverflow.com/a/446839

is there a Java equivalent to null coalescing operator (??) in C#?

Is there a VB.NET equivalent for C#&#39;s `??` operator?


Is there a VB.NET equivalent for C#&#39;s &#39;??&#39; operator?

Something I find myself doing more and more is checking a string for empty (as in `&quot;&quot;` or null) and a conditional operator.

A current example:

    s.SiteNumber.IsNullOrEmpty() ? &quot;No Number&quot; : s.SiteNumber;

This is just an extension method, it&#39;s equivalent to:

    string.IsNullOrEmpty(s.SiteNumber) ? &quot;No Number&quot; : s.SiteNumber;

Since it&#39;s empty and not null, `??` won&#39;t do the trick.  A `string.IsNullOrEmpty()` version of `??` would be the perfect solution.  I&#39;m thinking there has to be a cleaner way of doing this (I hope!), but I&#39;ve been at a loss to find it.  

Does anyone know of a better way to do this, even if it&#39;s only in .Net 4.0?

?? Coalesce for empty string?

I know the standard way of using the [null coalescing operator][1] in C# is to set default values.

    string nobody = null;
    string somebody = &quot;Bob Saget&quot;;
    string anybody = &quot;&quot;;

    anybody = nobody   ?? &quot;Mr. T&quot;; // Returns Mr. T
    anybody = somebody ?? &quot;Mr. T&quot;; // Returns &quot;Bob Saget&quot;

But what else can `??` be used for? It doesn&#39;t seem as useful as the [ternary operator][2], apart from being more concise and easier to read than:

    nobody = null;
    anybody = nobody == null ? &quot;Bob Saget&quot; : nobody; // Returns Bob Saget

So given that fewer even know about null coalescing operator...

 - Have you used `??` for something else?

 -  Is `??` necessary, or should you just use the ternary operator (that
   most are familiar with)

  [1]: https://en.wikipedia.org/wiki/Null_coalescing_operator
  [2]: https://en.wikipedia.org/wiki/%3F:




Unique ways to use the null coalescing operator

The line `price = co?.price ?? 0,` in the following code gives me the above error, but if I remove `?` from `co.?` it works fine. 

I was trying to follow [this MSDN example][1] where they are using `?` on line `select new { person.FirstName, PetName = subpet?.Name ?? String.Empty };` So, it seems I need to understand when to use `?` with `??` and when not to.

**Error**:

&gt;an expression tree lambda may not contain a null propagating operator

    public class CustomerOrdersModelView
    {
        public string CustomerID { get; set; }
        public int FY { get; set; }
        public float? price { get; set; }
        ....
        ....
    }
    public async Task&lt;IActionResult&gt; ProductAnnualReport(string rpt)
    {
        var qry = from c in _context.Customers
                  join ord in _context.Orders
                    on c.CustomerID equals ord.CustomerID into co
                  from m in co.DefaultIfEmpty()
                  select new CustomerOrdersModelView
                  {
                      CustomerID = c.CustomerID,
                      FY = c.FY,
                      price = co?.price ?? 0,
                      ....
                      ....
                  };
        ....
        ....
     }


  [1]: https://docs.microsoft.com/en-us/dotnet/csharp/linq/perform-left-outer-joins


An expression tree lambda may not contain a null propagating operator

Is there a null coalescing operator in powershell? 

I&#39;d like to be able to do these c# commands in powershell:

    var s = myval ?? &quot;new value&quot;;
    var x = myval == null ? &quot;&quot; : otherval;
 

Null coalescing in powershell

Many programming languages have a coalesce function (returns the first non-NULL value, [example](http://www.postgresql.org/docs/9.3/static/functions-conditional.html#FUNCTIONS-COALESCE-NVL-IFNULL)). PHP, sadly in 2009, does not.

What would be a good way to implement one in PHP until PHP itself gets a coalesce function?

Coalesce function for PHP?

I love the null-coalescing operator because it makes it easy to assign a default value for nullable types.

     int y = x ?? -1;

That&#39;s great, except if I need to do something simple with `x`. For instance, if I want to check `Session`, then I usually end up having to write something more verbose.

I wish I could do this:

    string y = Session[&quot;key&quot;].ToString() ?? &quot;none&quot;;

But you can&#39;t because the `.ToString()` gets called before the null check so it fails if `Session[&quot;key&quot;]` is null. I end up doing this:

    string y = Session[&quot;key&quot;] == null ? &quot;none&quot; : Session[&quot;key&quot;].ToString();

It works and is better, in my opinion, than the three-line alternative:

    string y = &quot;none&quot;;
    if (Session[&quot;key&quot;] != null)
        y = Session[&quot;key&quot;].ToString();

Even though that works I am still curious if there is a better way. It seems no matter what I always have to reference `Session[&quot;key&quot;]` twice; once for the check, and again for the assignment. Any ideas?

What is the proper way to check for null values?

**Note: this appears to have been fixed in [Roslyn][1]**

This question arose when writing my answer to [this one][2], which talks about the associativity of the [null-coalescing operator][3].

Just as a reminder, the idea of the null-coalescing operator is that an expression of the form

    x ?? y

first evaluates `x`, then:

- If the value of `x` is null, `y` is evaluated and that is the end result of the expression
- If the value of `x` is non-null, `y` is *not* evaluated, and the value of `x` is the end result of the expression, after a conversion to the compile-time type of `y` if necessary

Now *usually* there&#39;s no need for a conversion, or it&#39;s just from a nullable type to a non-nullable one - usually the types are the same, or just from (say) `int?` to `int`. However, you *can* create your own implicit conversion operators, and those are used where necessary.

For the simple case of `x ?? y`, I haven&#39;t seen any odd behaviour. However, with `(x ?? y) ?? z` I see some confusing behaviour.

Here&#39;s a short but complete test program - the results are in the comments:

    using System;
    
    public struct A
    {
        public static implicit operator B(A input)
        {
            Console.WriteLine(&quot;A to B&quot;);
            return new B();
        }
    
        public static implicit operator C(A input)
        {
            Console.WriteLine(&quot;A to C&quot;);
            return new C();
        }
    }
    
    public struct B
    {
        public static implicit operator C(B input)
        {
            Console.WriteLine(&quot;B to C&quot;);
            return new C();
        }
    }
    
    public struct C {}
    
    class Test
    {
        static void Main()
        {
            A? x = new A();
            B? y = new B();
            C? z = new C();
            C zNotNull = new C();
    
            Console.WriteLine(&quot;First case&quot;);
            // This prints
            // A to B
            // A to B
            // B to C
            C? first = (x ?? y) ?? z;
    
            Console.WriteLine(&quot;Second case&quot;);
            // This prints
            // A to B
            // B to C
            var tmp = x ?? y;
            C? second = tmp ?? z;
    
            Console.WriteLine(&quot;Third case&quot;);
            // This prints
            // A to B
            // B to C
            C? third = (x ?? y) ?? zNotNull;
        }
    }

So we have three custom value types, `A`, `B` and `C`, with conversions from A to B, A to C, and B to C.

I can understand both the second case and the third case... but *why* is there an extra A to B conversion in the first case? In particular, I&#39;d *really* have expected the first case and second case to be the same thing - it&#39;s just extracting an expression into a local variable, after all.

Any takers on what&#39;s going on? I&#39;m extremely hesistant to cry &quot;bug&quot; when it comes to the C# compiler, but I&#39;m stumped as to what&#39;s going on...

EDIT: Okay, here&#39;s a nastier example of what&#39;s going on, thanks to configurator&#39;s answer, which gives me further reason to think it&#39;s a bug. EDIT: The sample doesn&#39;t even need two null-coalescing operators now...

    using System;
    
    public struct A
    {
        public static implicit operator int(A input)
        {
            Console.WriteLine(&quot;A to int&quot;);
            return 10;
        }
    }
    
    class Test
    {
        static A? Foo()
        {
            Console.WriteLine(&quot;Foo() called&quot;);
            return new A();
        }
        
        static void Main()
        {
            int? y = 10;
            
            int? result = Foo() ?? y;
        }
    }

The output of this is:

    Foo() called
    Foo() called
    A to int

The fact that `Foo()` gets called twice here is hugely surprising to me - I can&#39;t see any reason for the expression to be *evaluated* twice.


  [1]: https://github.com/dotnet/roslyn
  [2]: https://stackoverflow.com/questions/6238074
  [3]: http://msdn.microsoft.com/en-us/library/ms173224.aspx

Curious null-coalescing operator custom implicit conversion behaviour

Can someone explain the differences between [ternary operator shorthand](https://www.php.net/manual/en/language.operators.comparison.php#language.operators.comparison.ternary) (`?:`) and [null coalescing operator](https://www.php.net/manual/en/language.operators.comparison.php#language.operators.comparison.coalesce) (`??`) in PHP?

When do they behave differently and when in the same way (if that even happens)?

    $a ?: $b

VS.

    $a ?? $b

PHP Elvis operator vs null coalescing operator

null coalescing translates roughly to `return x, unless it is null, in which case return y`

I often need `return null if x is null, otherwise return x.y`

I can use `return x == null ? null : x.y;`

Not bad, but that `null` in the middle always bothers me -- it seems superfluous. I&#39;d prefer something like `return x :: x.y;`, where what follows the `::` is evaluated only if what precedes it is not `null`.

I see this as *almost* an opposite to null coalescence, kind of mixed in with a terse, inline null-check, but I&#39;m [*almost*] certain that there is no such operator in C#.

### Are there other languages that have such an operator? If so, what is it called? ###


*(I know that I can write a method for it in C#; I use `return NullOrValue.of(x, () =&gt; x.y);`, but if you have anything better, I&#39;d like to see that too.)*

Is there an &quot;opposite&quot; to the null coalescing operator? (…in any language?)

While I was studying the _delegate_ which _is_ actually an abstract class in [`Delegate.cs`][1], I saw the following method in which I don&#39;t understand

 - Why the return value uses `?` though it&#39;s already a reference(_class_) type
 - `?[]?` meaning on the parameter

Could you explain?

    public static Delegate? Combine(params Delegate?[]? delegates)
    {
        if (delegates == null || delegates.Length == 0)
            return null;

        Delegate? d = delegates[0];
        for (int i = 1; i &lt; delegates.Length; i++)
            d = Combine(d, delegates[i]);

        return d;
    }

  [1]: https://github.com/dotnet/corert/blob/master/src/System.Private.CoreLib/shared/System/Delegate.cs


What is the ?[]? syntax in C#?

Ran across this line of code:

    FormsAuth = formsAuth ?? new FormsAuthenticationWrapper();

What do the two question marks mean, is it some kind of ternary operator?
It&#39;s hard to look up in Google.

What do two question marks together mean in C#?

In C# there&#39;s a [null-coalescing operator][1] (written as `??`) that allows for easy (short) null checking during assignment:

    string s = null;
    var other = s ?? &quot;some default value&quot;;

Is there a python equivalent?

I know that I can do:

    s = None
    other = s if s else &quot;some default value&quot;

But is there an even shorter way (where I don&#39;t need to repeat `s`)?


  [1]: http://msdn.microsoft.com/en-us/library/ms173224.aspx

Is there a Python equivalent of the C# null-coalescing operator?

What is the equivalent of null coalescing operator (??) in angular 2?

In C# we can perform this operation:

    string str = name ?? FirstName ?? &quot;First Name is null&quot;;

Null coalescing operator angular 2

&gt; **Possible Duplicates:**  
&gt; [?? Null Coalescing Operator --&amp;gt; What does coalescing mean?](https://stackoverflow.com/questions/770186/-null-coalescing-operator-what-does-coalescing-mean)  
&gt; [What do two question marks together mean in C#?](https://stackoverflow.com/questions/446835/what-do-two-question-marks-together-mean-in-c)  


I couldn&#39;t find this question being asked here so I figured I would ask it. What does a double question mark do in C#?

Example:

    x = y ?? z;

What does a double question mark do in C#?

&gt; **Possible Duplicates:**  
&gt; [Coalesce operator and Conditional operator in VB.NET](https://stackoverflow.com/questions/629036/coalesce-operator-and-conditional-operator-in-vb-net)  
&gt; [Is there a VB.NET equivalent for C#&amp;#39;s ?? operator?](https://stackoverflow.com/questions/403445/is-there-a-vb-net-equivalent-for-cs-operator)  

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

Is there a built-in VB.NET equivalent to the C# null coalescing operator?

VB.NET null coalescing operator?

I&#39;m writing a piece of code in c#6 and for some strange reason this works

    var value = objectThatMayBeNull?.property;

but this doesn&#39;t:

    int value = nullableInt?.Value;

By not works I mean I get a compile error saying `Cannot resolve symbol &#39;Value&#39;`.
Any idea why the null conditional operator `?.` isn&#39;t working?

null conditional operator not working with nullable types?

Is there a null coalescing operator in Javascript?

For example, in C#, I can do this:

    String someString = null;
    var whatIWant = someString ?? &quot;Cookies!&quot;;

The best approximation I can figure out for Javascript is using the conditional operator:

    var someString = null;
    var whatIWant = someString ? someString : &#39;Cookies!&#39;;

Which is sorta icky IMHO. Can I do better?

Is there a &quot;null coalescing&quot; operator in JavaScript?

How can I write a shorthand of the following scenario?

    get
    {
        if (_rows == null)
        {
            _rows = new List&lt;Row&gt;();
        }

        return _rows;
    }



Is there a shorthand way to return values that might be null?

I&#39;m tempted to lie and say that English is my second language, but the truth is that I just have no idea what &#39;Coalescing&#39; means.  I know what `??` &#39;does&#39; in C#, but the name doesn&#39;t make sense to me.

I looked up the word and I understand it to be a synonym for &#39;join&#39;.  &#39;Null Join Operator&#39; still doesn&#39;t make sense.

Can someone enlighten me?

All Null Coalescing-Operator Solutions on Gang of Coders

Total of 22 Null Coalescing-Operator Solutions

C#'s null coalescing operator (??) in PHP