C is keyword and checking for Not

Question

This is a silly question  but you can use this code to check if something is a particular type     if  child is IContainer             Is there a more elegant way to check for the  NOT  instance   if    child is IContainer       A little ugly    silly  yes I know       these don t work    if  child  is IContainer    if  child isnt IContainer     if  child aint IContainer     if  child isnotafreaking IContainer       Yes  yes    silly question      Because there is some question on what the code looks like  it s just a simple return at the start of a method   public void Update DocumentPart part        part Update        if    DocumentPart is IContainer     return        foreach DocumentPart child in   IContainer part  Children                etc

User · Answer

The extension method IsNot lt T gt  is a nice way to extend the syntax  Keep in mind  var container   child as IContainer  if container    null         do something w  contianer     performs better than doing something like  if child is IContainer      var container   child as IContainer       do something w  container     In your case  it doesn t matter as you are returning from the method  In other words  be careful to not do both the check for type and then the type conversion immediately after

User · Answer

Ugly  I disagree  The only other way  I personally think this is  uglier     var obj   child as IContainer  if obj    null         child  aint  IContainer

User · Answer

You can do it this way   object a   new StreamWriter  c   temp  test txt     if  a is TextReader    false       Console WriteLine  failed

User · Answer

This hasn t been mentioned yet  It works and I think it looks better than using   child is IContainer  if  part is IContainer is false        return     New In C  9 0 https   devblogs microsoft com dotnet welcome-to-c-9-0  logical-patterns if  part is not IContainer        return

User · Answer

if   child is IContainer     is the only operator to go  there s no IsNot operator    You can build an extension method that does it   public static bool IsA lt T gt  this object obj        return obj is T      and then use it to   if   child IsA lt IContainer gt       And you could follow on your theme   public static bool IsNotAFreaking lt T gt  this object obj        return   obj is T      if  child IsNotAFreaking lt IContainer gt                  Update  considering the OP s code snippet    Since you re actually casting the value afterward  you could just use as instead   public void Update DocumentPart part        part Update        IContainer containerPart   part as IContainer      if containerPart    null  return      foreach DocumentPart child in containerPart Children       omit the cast              etc

User · Answer

While the IS operator is normally the best way  there is an alternative that you can use in some cirumstances   You can use the as operator and test for null   MyClass mc   foo as MyClass  if   mc    null       else

User · Answer

The is operator evaluates to a boolean result  so you can do anything you would otherwise be able to do on a bool  To negate it use the   operator  Why would you want to have a  different operator just for this

User · Answer

The way you have it is fine but you could create a set of extension methods to make  a more elegant way to check for the  NOT  instance    public static bool Is lt T gt  this object myObject        return  myObject is T      public static bool IsNot lt T gt  this object myObject        return   myObject is T       Then you could write   if  child IsNot lt IContainer gt              child is not an IContainer

User · Answer

if  child is IContainer   false   true

User · Answer

While this doesn t avoid the problem of parentheses  for the sake of people getting here via Google  it should be mentioned that newer syntax exists  as of C  7  to make the rest of your code a little cleaner   if    DocumentPart is IContainer container     return    foreach DocumentPart child in container Children              This avoids the double-cast  the null-check  and having a variable available in scopes where it could be null

User · Answer

Why not just use the else    if  child is IContainer           else        Do what you want here     Its neat it familiar and simple

User · Answer

C  9  released with  NET 5  includes the logical patterns and  or and not  which allows us to write this more elegantly  if  child is not IContainer           Likewise  this pattern can be used to check for null  if  child is not null

[c#] C# : 'is' keyword and checking for Not

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