Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>I remember this behavior was kind of last minute change. In early betas of .NET 2.0, <code>Nullable&lt;T&gt;</code> was a "normal" value type. Boxing a <code>null</code> valued <code>int?</code> turned it into a boxed <code>int?</code> with a boolean flag. I think the reason they decided to choose the current approach is consistency. Say:</p> <pre><code>int? test = null; object obj = test; if (test != null) Console.WriteLine("test is not null"); if (obj != null) Console.WriteLine("obj is not null"); </code></pre> <p>In the former approach (box <code>null</code> -> boxed <code>Nullable&lt;T&gt;</code>), you wouldn't get "test is not null" but you'd get "object is not null" which is weird. </p> <p>Additionally, if they had boxed a nullable value to a <code>boxed-Nullable&lt;T&gt;</code>:</p> <pre><code>int? val = 42; object obj = val; if (obj != null) { // Our object is not null, so intuitively it's an `int` value: int x = (int)obj; // ...but this would have failed. } </code></pre> <p>Beside that, I believe the current behavior makes perfect sense for scenarios like nullable database values (think SQL-CLR...)</p> <hr> <h3>Clarification:</h3> <p>The whole point of providing nullable types is to make it easy to deal with variables that have no meaningful value. They didn't want to provide two distinct, unrelated types. An <code>int?</code> should behaved more or less like a simple <code>int</code>. That's why C# provides lifted operators. </p> <blockquote> <p>So, when unboxing a value type into a nullable version, the CLR must allocate a <code>Nullable&lt;T&gt;</code> object, initialize the hasValue field to true, and set the value field to the same value that is in the boxed value type. This impacts your application performance (memory allocation during unboxing).</p> </blockquote> <p>This is not true. The CLR would have to allocates memory <strong>on stack</strong> to hold the variable whether or not it's nullable. There's not a performance issue to allocate space for an extra boolean variable.</p>
    singulars
    1. This table or related slice is empty.
    1. POBoxing / Unboxing Nullable Types - Why this implementation?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USMehrdad Afshari
    1. USMehrdad Afshari
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POBoxing / Unboxing Nullable Types - Why this implementation?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COFrom what I understand, in the current implementation (Step 1) if test is null, the CLR does not box anything and returns null. (Step 2) If the nullable instance is not null, it boxes it into a boxed-int32. Doesn't Step 1 solve the "obj is not null" problem? Why did they have to do step 2 ? Sorry, but I seem to be missing something.
      singulars
      1. PO
      1. USPreets
    2. COPreets: You mean they would box `null` to a null reference and box `int? x = 4;` to `boxed-Nullable<int>`?
      singulars
      1. PO
      1. USMehrdad Afshari
    3. COUmm.. yeah.. is that not possible ?
      singulars
      1. PO
      1. USPreets
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload