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kotlin.reflect.KClass.isInstance(value: Any?) not working

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0

I'm trying the follow

"simple string"::class.isInstance(kotlin.String)

But it return false!

I'm using

"org.jetbrains.kotlin:kotlin-reflect:1.3.21"

The another examples also fail

1::class.isInstance(kotlin.Int)
true::class.isInstance(Boolean)

Please, help me to understand it!

class kotlin reflection instanceof

share|improve this question

asked Mar 27 at 21:23

Abner EscócioAbner Escócio

1,37711 gold badge88 silver badges2222 bronze badges

add a comment | 

0

I'm trying the follow

"simple string"::class.isInstance(kotlin.String)

But it return false!

I'm using

"org.jetbrains.kotlin:kotlin-reflect:1.3.21"

The another examples also fail

1::class.isInstance(kotlin.Int)
true::class.isInstance(Boolean)

Please, help me to understand it!

class kotlin reflection instanceof

share|improve this question

asked Mar 27 at 21:23

Abner EscócioAbner Escócio

1,37711 gold badge88 silver badges2222 bronze badges

add a comment | 

I'm trying the follow

"simple string"::class.isInstance(kotlin.String)

But it return false!

I'm using

"org.jetbrains.kotlin:kotlin-reflect:1.3.21"

The another examples also fail

1::class.isInstance(kotlin.Int)
true::class.isInstance(Boolean)

Please, help me to understand it!

class kotlin reflection instanceof

share|improve this question

asked Mar 27 at 21:23

Abner EscócioAbner Escócio

1,37711 gold badge88 silver badges2222 bronze badges

"simple string"::class.isInstance(kotlin.String)

1::class.isInstance(kotlin.Int)
true::class.isInstance(Boolean)

share|improve this question

asked Mar 27 at 21:23

Abner EscócioAbner Escócio

1,37711 gold badge88 silver badges2222 bronze badges

share|improve this question

asked Mar 27 at 21:23

Abner EscócioAbner Escócio

1,37711 gold badge88 silver badges2222 bronze badges

asked Mar 27 at 21:23

Abner EscócioAbner Escócio

1,37711 gold badge88 silver badges2222 bronze badges

asked Mar 27 at 21:23

Abner EscócioAbner Escócio

1,37711 gold badge88 silver badges2222 bronze badges

2 Answers
2

active

oldest

votes

1

You use the API incorrectly, the isInstance function does the opposite check as shown in the documentation:

Returns true if [value] is an instance of this class on a given platform.

The kotlin.Int line does not refer to a type, you miss the ::class.

A possible solution is to flip the declaration:

String::class.isInstance("a string") /// true
Int::class.isInstance(42) /// true

You may also compare KClass objects, e.g. 432::class == Int::class or use KClass functions isSubclassOf and isSuperclassOf

share|improve this answer

answered Mar 27 at 22:55

Eugene PetrenkoEugene Petrenko

3,2831818 silver badges2727 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  432::class == Int::class it work but Int::class.isInstance(42) not. Thanks!
  
  – Abner Escócio
  Mar 28 at 4:38
  

  
  
  
  

add a comment | 

2

kotlin.String, kotlin.Int, and Boolean are used as values, so they refer to companion objects of the corresponding classes. So the first line checks whether the String companion object is a String and correctly tells you it isn't.

share|improve this answer

answered Mar 28 at 4:28

Alexey RomanovAlexey Romanov

118k2727 gold badges224224 silver badges368368 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I was looking for a Java's Class#isAssignableFrom(obj) function analog. It is interesting to spot that kotlin.Int means companion object, but kotlin.Int::class means the KClass of not (and not a KClass of the companion)
  
  – Eugene Petrenko
  Mar 28 at 8:45
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @EugenePetrenko Do you mean Class#isAssignableFrom(Class<?>)? That would be kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect.full/… (and nicely, there's a symmetric isSubclassOf).
  
  – Alexey Romanov
  Mar 28 at 17:08
  

  
  
  
  

add a comment | 

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1

You use the API incorrectly, the isInstance function does the opposite check as shown in the documentation:

Returns true if [value] is an instance of this class on a given platform.

The kotlin.Int line does not refer to a type, you miss the ::class.

A possible solution is to flip the declaration:

String::class.isInstance("a string") /// true
Int::class.isInstance(42) /// true

You may also compare KClass objects, e.g. 432::class == Int::class or use KClass functions isSubclassOf and isSuperclassOf

share|improve this answer

answered Mar 27 at 22:55

Eugene PetrenkoEugene Petrenko

3,2831818 silver badges2727 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  432::class == Int::class it work but Int::class.isInstance(42) not. Thanks!
  
  – Abner Escócio
  Mar 28 at 4:38
  

  
  
  
  

add a comment | 

1

You use the API incorrectly, the isInstance function does the opposite check as shown in the documentation:

Returns true if [value] is an instance of this class on a given platform.

The kotlin.Int line does not refer to a type, you miss the ::class.

A possible solution is to flip the declaration:

String::class.isInstance("a string") /// true
Int::class.isInstance(42) /// true

You may also compare KClass objects, e.g. 432::class == Int::class or use KClass functions isSubclassOf and isSuperclassOf

share|improve this answer

answered Mar 27 at 22:55

Eugene PetrenkoEugene Petrenko

3,2831818 silver badges2727 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  432::class == Int::class it work but Int::class.isInstance(42) not. Thanks!
  
  – Abner Escócio
  Mar 28 at 4:38
  

  
  
  
  

add a comment | 

You use the API incorrectly, the isInstance function does the opposite check as shown in the documentation:

Returns true if [value] is an instance of this class on a given platform.

The kotlin.Int line does not refer to a type, you miss the ::class.

A possible solution is to flip the declaration:

String::class.isInstance("a string") /// true
Int::class.isInstance(42) /// true

You may also compare KClass objects, e.g. 432::class == Int::class or use KClass functions isSubclassOf and isSuperclassOf

share|improve this answer

answered Mar 27 at 22:55

Eugene PetrenkoEugene Petrenko

3,2831818 silver badges2727 bronze badges

String::class.isInstance("a string") /// true
Int::class.isInstance(42) /// true

share|improve this answer

answered Mar 27 at 22:55

Eugene PetrenkoEugene Petrenko

3,2831818 silver badges2727 bronze badges

answered Mar 27 at 22:55

Eugene PetrenkoEugene Petrenko

3,2831818 silver badges2727 bronze badges

answered Mar 27 at 22:55

Eugene PetrenkoEugene Petrenko

3,2831818 silver badges2727 bronze badges

2

kotlin.String, kotlin.Int, and Boolean are used as values, so they refer to companion objects of the corresponding classes. So the first line checks whether the String companion object is a String and correctly tells you it isn't.

share|improve this answer

answered Mar 28 at 4:28

Alexey RomanovAlexey Romanov

118k2727 gold badges224224 silver badges368368 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I was looking for a Java's Class#isAssignableFrom(obj) function analog. It is interesting to spot that kotlin.Int means companion object, but kotlin.Int::class means the KClass of not (and not a KClass of the companion)
  
  – Eugene Petrenko
  Mar 28 at 8:45
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @EugenePetrenko Do you mean Class#isAssignableFrom(Class<?>)? That would be kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect.full/… (and nicely, there's a symmetric isSubclassOf).
  
  – Alexey Romanov
  Mar 28 at 17:08
  

  
  
  
  

add a comment | 

2

kotlin.String, kotlin.Int, and Boolean are used as values, so they refer to companion objects of the corresponding classes. So the first line checks whether the String companion object is a String and correctly tells you it isn't.

share|improve this answer

answered Mar 28 at 4:28

Alexey RomanovAlexey Romanov

118k2727 gold badges224224 silver badges368368 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I was looking for a Java's Class#isAssignableFrom(obj) function analog. It is interesting to spot that kotlin.Int means companion object, but kotlin.Int::class means the KClass of not (and not a KClass of the companion)
  
  – Eugene Petrenko
  Mar 28 at 8:45
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  @EugenePetrenko Do you mean Class#isAssignableFrom(Class<?>)? That would be kotlinlang.org/api/latest/jvm/stdlib/kotlin.reflect.full/… (and nicely, there's a symmetric isSubclassOf).
  
  – Alexey Romanov
  Mar 28 at 17:08
  

  
  
  
  

add a comment | 

kotlin.String, kotlin.Int, and Boolean are used as values, so they refer to companion objects of the corresponding classes. So the first line checks whether the String companion object is a String and correctly tells you it isn't.

share|improve this answer

answered Mar 28 at 4:28

Alexey RomanovAlexey Romanov

118k2727 gold badges224224 silver badges368368 bronze badges

share|improve this answer

answered Mar 28 at 4:28

Alexey RomanovAlexey Romanov

118k2727 gold badges224224 silver badges368368 bronze badges

answered Mar 28 at 4:28

Alexey RomanovAlexey Romanov

118k2727 gold badges224224 silver badges368368 bronze badges

answered Mar 28 at 4:28

Alexey RomanovAlexey Romanov

118k2727 gold badges224224 silver badges368368 bronze badges