is vs typeof

Question

Which of these pieces of code is faster   if  obj is ClassA      if  obj GetType      typeof ClassA        Edit  I m aware that they don t do the same thing

User · Accepted Answer

This should answer that question  and then some   The second line  if  obj GetType      typeof ClassA       is faster  for those that don t want to read the article    Be aware that they don t do the same thing

User · Answer

They don t do the same thing   The first one works if obj is of type ClassA or of some subclass of ClassA   The second one will only match objects of type ClassA   The second one will be faster since it doesn t have to check the class hierarchy   For those who want to know the reason  but don t want to read the article referenced in is vs typeof

User · Answer

Does it matter which is faster  if they don t do the same thing   Comparing the performance of statements with different meaning seems like a bad idea   is tells you if the object implements ClassA anywhere in its type heirarchy   GetType   tells you about the most-derived type   Not the same thing

User · Answer

I did some benchmarking where they do the same - sealed types   var c1       var c2   typeof string   object oc1   c1  object oc2   c2   var s1   0  var s2        object os1   s1  object os2   s2   bool b   false   Stopwatch sw   Stopwatch StartNew    for  int i   0  i  lt  10000000  i          b   c1 GetType      typeof string       60ms     b   c1 is string      60ms      b   c2 GetType      typeof string       60ms     b   c2 is string      50ms      b   oc1 GetType      typeof string       60ms     b   oc1 is string      68ms      b   oc2 GetType      typeof string       60ms     b   oc2 is string      64ms       b   s1 GetType      typeof int       130ms     b   s1 is int      50ms      b   s2 GetType      typeof int       140ms     b   s2 is int      50ms      b   os1 GetType      typeof int       60ms     b   os1 is int      74ms      b   os2 GetType      typeof int       60ms     b   os2 is int      68ms       b   GetType1 lt string  string gt  c1       178ms     b   GetType2 lt string  string gt  c1       94ms     b   Is lt string  string gt  c1       70ms      b   GetType1 lt string  Type gt  c2       178ms     b   GetType2 lt string  Type gt  c2       96ms     b   Is lt string  Type gt  c2       65ms      b   GetType1 lt string  object gt  oc1       190ms     b   Is lt string  object gt  oc1       69ms      b   GetType1 lt string  object gt  oc2       180ms     b   Is lt string  object gt  oc2       64ms       b   GetType1 lt int  int gt  s1       230ms     b   GetType2 lt int  int gt  s1       75ms     b   Is lt int  int gt  s1       136ms      b   GetType1 lt int  char gt  s2       238ms     b   GetType2 lt int  char gt  s2       69ms     b   Is lt int  char gt  s2       142ms      b   GetType1 lt int  object gt  os1       178ms     b   Is lt int  object gt  os1       69ms      b   GetType1 lt int  object gt  os2       178ms     b   Is lt int  object gt  os2       69ms    sw Stop    MessageBox Show sw Elapsed TotalMilliseconds ToString       The generic functions to test for generic types   static bool GetType1 lt S  T gt  T t        return t GetType      typeof S     static bool GetType2 lt S  T gt  T t        return typeof T     typeof S     static bool Is lt S  T gt  T t        return t is S      I tried for custom types as well and the results were consistent    var c1   new Class1    var c2   new Class2    object oc1   c1  object oc2   c2   var s1   new Struct1    var s2   new Struct2    object os1   s1  object os2   s2   bool b   false   Stopwatch sw   Stopwatch StartNew    for  int i   0  i  lt  10000000  i          b   c1 GetType      typeof Class1       60ms     b   c1 is Class1      60ms      b   c2 GetType      typeof Class1       60ms     b   c2 is Class1      55ms      b   oc1 GetType      typeof Class1       60ms     b   oc1 is Class1      68ms      b   oc2 GetType      typeof Class1       60ms     b   oc2 is Class1      68ms       b   s1 GetType      typeof Struct1       150ms     b   s1 is Struct1      50ms      b   s2 GetType      typeof Struct1       150ms     b   s2 is Struct1      50ms      b   os1 GetType      typeof Struct1       60ms     b   os1 is Struct1      64ms      b   os2 GetType      typeof Struct1       60ms     b   os2 is Struct1      64ms       b   GetType1 lt Class1  Class1 gt  c1       178ms     b   GetType2 lt Class1  Class1 gt  c1       98ms     b   Is lt Class1  Class1 gt  c1       78ms      b   GetType1 lt Class1  Class2 gt  c2       178ms     b   GetType2 lt Class1  Class2 gt  c2       96ms     b   Is lt Class1  Class2 gt  c2       69ms      b   GetType1 lt Class1  object gt  oc1       178ms     b   Is lt Class1  object gt  oc1       69ms      b   GetType1 lt Class1  object gt  oc2       178ms     b   Is lt Class1  object gt  oc2       69ms       b   GetType1 lt Struct1  Struct1 gt  s1       272ms     b   GetType2 lt Struct1  Struct1 gt  s1       140ms     b   Is lt Struct1  Struct1 gt  s1       163ms      b   GetType1 lt Struct1  Struct2 gt  s2       272ms     b   GetType2 lt Struct1  Struct2 gt  s2       140ms     b   Is lt Struct1  Struct2 gt  s2       163ms      b   GetType1 lt Struct1  object gt  os1       178ms     b   Is lt Struct1  object gt  os1       64ms      b   GetType1 lt Struct1  object gt  os2       178ms     b   Is lt Struct1  object gt  os2       64ms    sw Stop    MessageBox Show sw Elapsed TotalMilliseconds ToString       And the types   sealed class Class1     sealed class Class2     struct Struct1     struct Struct2       Inference    Calling GetType on structs is slower  GetType is defined on object class which can t be overridden in sub types and thus structs need to be boxed to be called GetType   On an object instance  GetType is faster  but very marginally  On generic type  if T is class  then is is much faster  If T is struct  then is is much faster than GetType but typeof T  is much faster than both  In cases of T being class  typeof T  is not reliable since its different from actual underlying type t GetType    In short  if you have an object instance  use GetType  If you have a generic class type  use is  If you have a generic struct type  use typeof T   If you are unsure if generic type is reference type or value type  use is  If you want to be consistent with one style always  for sealed types   use is

User · Answer

They don t do the same thing   The first one works if obj is of type ClassA or of some subclass of ClassA   The second one will only match objects of type ClassA   The second one will be faster since it doesn t have to check the class hierarchy   For those who want to know the reason  but don t want to read the article referenced in is vs typeof

User · Answer

They don t do the same thing   The first one works if obj is of type ClassA or of some subclass of ClassA   The second one will only match objects of type ClassA   The second one will be faster since it doesn t have to check the class hierarchy   For those who want to know the reason  but don t want to read the article referenced in is vs typeof

User · Answer

Does it matter which is faster  if they don t do the same thing   Comparing the performance of statements with different meaning seems like a bad idea   is tells you if the object implements ClassA anywhere in its type heirarchy   GetType   tells you about the most-derived type   Not the same thing

User · Answer

Does it matter which is faster  if they don t do the same thing   Comparing the performance of statements with different meaning seems like a bad idea   is tells you if the object implements ClassA anywhere in its type heirarchy   GetType   tells you about the most-derived type   Not the same thing

User · Answer

They don t do the same thing   The first one works if obj is of type ClassA or of some subclass of ClassA   The second one will only match objects of type ClassA   The second one will be faster since it doesn t have to check the class hierarchy   For those who want to know the reason  but don t want to read the article referenced in is vs typeof

User · Answer

Does it matter which is faster  if they don t do the same thing   Comparing the performance of statements with different meaning seems like a bad idea   is tells you if the object implements ClassA anywhere in its type heirarchy   GetType   tells you about the most-derived type   Not the same thing

User · Answer

I did some benchmarking where they do the same - sealed types   var c1       var c2   typeof string   object oc1   c1  object oc2   c2   var s1   0  var s2        object os1   s1  object os2   s2   bool b   false   Stopwatch sw   Stopwatch StartNew    for  int i   0  i  lt  10000000  i          b   c1 GetType      typeof string       60ms     b   c1 is string      60ms      b   c2 GetType      typeof string       60ms     b   c2 is string      50ms      b   oc1 GetType      typeof string       60ms     b   oc1 is string      68ms      b   oc2 GetType      typeof string       60ms     b   oc2 is string      64ms       b   s1 GetType      typeof int       130ms     b   s1 is int      50ms      b   s2 GetType      typeof int       140ms     b   s2 is int      50ms      b   os1 GetType      typeof int       60ms     b   os1 is int      74ms      b   os2 GetType      typeof int       60ms     b   os2 is int      68ms       b   GetType1 lt string  string gt  c1       178ms     b   GetType2 lt string  string gt  c1       94ms     b   Is lt string  string gt  c1       70ms      b   GetType1 lt string  Type gt  c2       178ms     b   GetType2 lt string  Type gt  c2       96ms     b   Is lt string  Type gt  c2       65ms      b   GetType1 lt string  object gt  oc1       190ms     b   Is lt string  object gt  oc1       69ms      b   GetType1 lt string  object gt  oc2       180ms     b   Is lt string  object gt  oc2       64ms       b   GetType1 lt int  int gt  s1       230ms     b   GetType2 lt int  int gt  s1       75ms     b   Is lt int  int gt  s1       136ms      b   GetType1 lt int  char gt  s2       238ms     b   GetType2 lt int  char gt  s2       69ms     b   Is lt int  char gt  s2       142ms      b   GetType1 lt int  object gt  os1       178ms     b   Is lt int  object gt  os1       69ms      b   GetType1 lt int  object gt  os2       178ms     b   Is lt int  object gt  os2       69ms    sw Stop    MessageBox Show sw Elapsed TotalMilliseconds ToString       The generic functions to test for generic types   static bool GetType1 lt S  T gt  T t        return t GetType      typeof S     static bool GetType2 lt S  T gt  T t        return typeof T     typeof S     static bool Is lt S  T gt  T t        return t is S      I tried for custom types as well and the results were consistent    var c1   new Class1    var c2   new Class2    object oc1   c1  object oc2   c2   var s1   new Struct1    var s2   new Struct2    object os1   s1  object os2   s2   bool b   false   Stopwatch sw   Stopwatch StartNew    for  int i   0  i  lt  10000000  i          b   c1 GetType      typeof Class1       60ms     b   c1 is Class1      60ms      b   c2 GetType      typeof Class1       60ms     b   c2 is Class1      55ms      b   oc1 GetType      typeof Class1       60ms     b   oc1 is Class1      68ms      b   oc2 GetType      typeof Class1       60ms     b   oc2 is Class1      68ms       b   s1 GetType      typeof Struct1       150ms     b   s1 is Struct1      50ms      b   s2 GetType      typeof Struct1       150ms     b   s2 is Struct1      50ms      b   os1 GetType      typeof Struct1       60ms     b   os1 is Struct1      64ms      b   os2 GetType      typeof Struct1       60ms     b   os2 is Struct1      64ms       b   GetType1 lt Class1  Class1 gt  c1       178ms     b   GetType2 lt Class1  Class1 gt  c1       98ms     b   Is lt Class1  Class1 gt  c1       78ms      b   GetType1 lt Class1  Class2 gt  c2       178ms     b   GetType2 lt Class1  Class2 gt  c2       96ms     b   Is lt Class1  Class2 gt  c2       69ms      b   GetType1 lt Class1  object gt  oc1       178ms     b   Is lt Class1  object gt  oc1       69ms      b   GetType1 lt Class1  object gt  oc2       178ms     b   Is lt Class1  object gt  oc2       69ms       b   GetType1 lt Struct1  Struct1 gt  s1       272ms     b   GetType2 lt Struct1  Struct1 gt  s1       140ms     b   Is lt Struct1  Struct1 gt  s1       163ms      b   GetType1 lt Struct1  Struct2 gt  s2       272ms     b   GetType2 lt Struct1  Struct2 gt  s2       140ms     b   Is lt Struct1  Struct2 gt  s2       163ms      b   GetType1 lt Struct1  object gt  os1       178ms     b   Is lt Struct1  object gt  os1       64ms      b   GetType1 lt Struct1  object gt  os2       178ms     b   Is lt Struct1  object gt  os2       64ms    sw Stop    MessageBox Show sw Elapsed TotalMilliseconds ToString       And the types   sealed class Class1     sealed class Class2     struct Struct1     struct Struct2       Inference    Calling GetType on structs is slower  GetType is defined on object class which can t be overridden in sub types and thus structs need to be boxed to be called GetType   On an object instance  GetType is faster  but very marginally  On generic type  if T is class  then is is much faster  If T is struct  then is is much faster than GetType but typeof T  is much faster than both  In cases of T being class  typeof T  is not reliable since its different from actual underlying type t GetType    In short  if you have an object instance  use GetType  If you have a generic class type  use is  If you have a generic struct type  use typeof T   If you are unsure if generic type is reference type or value type  use is  If you want to be consistent with one style always  for sealed types   use is

[c#] is vs typeof

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