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1

1

I want to map one object's property that has an enum type to another object's property that is other enum type.

I've tried with type1.a as Enum2 or Enum2[type1.a] with no success.

Here is my simplified code problem:

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.A
;

const type2: Type2 = 
 a: type1.a
;

try it

Throws the error:

Type 'Enum1' is not assignable to type 'Enum2'.
(property) Type2.a: Enum2

typescript enums casting

share|improve this question

edited Apr 2 at 8:44

AlbertoFdzM

64688 silver badges2121 bronze badges

asked Mar 27 at 10:07

Alex WeheAlex Wehe

1855 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I'm not sure at 100%, but the compiler correctly refuses the cast: what should happen when the a field becomes "N"? the Enum2 does not allow "N" as possible value. However, if you really want to cast two incompatible types, you may cast one to "any" first, then follow a second cast to Enum2...at your own risk!
  
  – Mario Vernari
  Mar 27 at 10:16
  

  
  
  
  

add a comment | 

1

1

I want to map one object's property that has an enum type to another object's property that is other enum type.

I've tried with type1.a as Enum2 or Enum2[type1.a] with no success.

Here is my simplified code problem:

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.A
;

const type2: Type2 = 
 a: type1.a
;

try it

Throws the error:

Type 'Enum1' is not assignable to type 'Enum2'.
(property) Type2.a: Enum2

typescript enums casting

share|improve this question

edited Apr 2 at 8:44

AlbertoFdzM

64688 silver badges2121 bronze badges

asked Mar 27 at 10:07

Alex WeheAlex Wehe

1855 bronze badges

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  I'm not sure at 100%, but the compiler correctly refuses the cast: what should happen when the a field becomes "N"? the Enum2 does not allow "N" as possible value. However, if you really want to cast two incompatible types, you may cast one to "any" first, then follow a second cast to Enum2...at your own risk!
  
  – Mario Vernari
  Mar 27 at 10:16
  

  
  
  
  

add a comment | 

I want to map one object's property that has an enum type to another object's property that is other enum type.

I've tried with type1.a as Enum2 or Enum2[type1.a] with no success.

Here is my simplified code problem:

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.A
;

const type2: Type2 = 
 a: type1.a
;

try it

Throws the error:

Type 'Enum1' is not assignable to type 'Enum2'.
(property) Type2.a: Enum2

typescript enums casting

share|improve this question

edited Apr 2 at 8:44

AlbertoFdzM

64688 silver badges2121 bronze badges

asked Mar 27 at 10:07

Alex WeheAlex Wehe

1855 bronze badges

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.A
;

const type2: Type2 = 
 a: type1.a
;

Type 'Enum1' is not assignable to type 'Enum2'.
(property) Type2.a: Enum2

share|improve this question

edited Apr 2 at 8:44

AlbertoFdzM

64688 silver badges2121 bronze badges

asked Mar 27 at 10:07

Alex WeheAlex Wehe

1855 bronze badges

share|improve this question

edited Apr 2 at 8:44

AlbertoFdzM

64688 silver badges2121 bronze badges

asked Mar 27 at 10:07

Alex WeheAlex Wehe

1855 bronze badges

edited Apr 2 at 8:44

AlbertoFdzM

64688 silver badges2121 bronze badges

edited Apr 2 at 8:44

AlbertoFdzM

64688 silver badges2121 bronze badges

asked Mar 27 at 10:07

Alex WeheAlex Wehe

1855 bronze badges

asked Mar 27 at 10:07

Alex WeheAlex Wehe

1855 bronze badges

1 Answer
1

active

oldest

votes

0

You need to cast the type1.a prop to Enum2. To do this you need to use a "Type Guard".

Here is an example with your code:

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.N
;

function isEnum2(value: any): value is Enum2 
 let isEnum2 = false;

 for (let key in Enum2) 
 if (Enum2[key] === value) 
 isEnum2 = true;
 
 

 return isEnum2;


if (isEnum2(type1.a)) 
 const type2: Type2 = 
 a: type1.a
 ;

try it

When the isEnum2 function is used in the if block the prop type1.a becomes of type Enum2 inside that if block only.

Note: you could replace the content in the isEnum2 using for..in loop if you are using ES2017 or higher using Object.values:

return Object.values(Enum2).indexOf(value) > -1;

try it (Doesn't work in www.typescriptlang.org)

More info about Type Guards

share|improve this answer

answered Mar 27 at 10:33

AlbertoFdzMAlbertoFdzM

64688 silver badges2121 bronze badges

add a comment | 

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0

You need to cast the type1.a prop to Enum2. To do this you need to use a "Type Guard".

Here is an example with your code:

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.N
;

function isEnum2(value: any): value is Enum2 
 let isEnum2 = false;

 for (let key in Enum2) 
 if (Enum2[key] === value) 
 isEnum2 = true;
 
 

 return isEnum2;


if (isEnum2(type1.a)) 
 const type2: Type2 = 
 a: type1.a
 ;

try it

When the isEnum2 function is used in the if block the prop type1.a becomes of type Enum2 inside that if block only.

Note: you could replace the content in the isEnum2 using for..in loop if you are using ES2017 or higher using Object.values:

return Object.values(Enum2).indexOf(value) > -1;

try it (Doesn't work in www.typescriptlang.org)

More info about Type Guards

share|improve this answer

answered Mar 27 at 10:33

AlbertoFdzMAlbertoFdzM

64688 silver badges2121 bronze badges

add a comment | 

0

You need to cast the type1.a prop to Enum2. To do this you need to use a "Type Guard".

Here is an example with your code:

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.N
;

function isEnum2(value: any): value is Enum2 
 let isEnum2 = false;

 for (let key in Enum2) 
 if (Enum2[key] === value) 
 isEnum2 = true;
 
 

 return isEnum2;


if (isEnum2(type1.a)) 
 const type2: Type2 = 
 a: type1.a
 ;

try it

When the isEnum2 function is used in the if block the prop type1.a becomes of type Enum2 inside that if block only.

Note: you could replace the content in the isEnum2 using for..in loop if you are using ES2017 or higher using Object.values:

return Object.values(Enum2).indexOf(value) > -1;

try it (Doesn't work in www.typescriptlang.org)

More info about Type Guards

share|improve this answer

answered Mar 27 at 10:33

AlbertoFdzMAlbertoFdzM

64688 silver badges2121 bronze badges

add a comment | 

You need to cast the type1.a prop to Enum2. To do this you need to use a "Type Guard".

Here is an example with your code:

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.N
;

function isEnum2(value: any): value is Enum2 
 let isEnum2 = false;

 for (let key in Enum2) 
 if (Enum2[key] === value) 
 isEnum2 = true;
 
 

 return isEnum2;


if (isEnum2(type1.a)) 
 const type2: Type2 = 
 a: type1.a
 ;

try it

When the isEnum2 function is used in the if block the prop type1.a becomes of type Enum2 inside that if block only.

Note: you could replace the content in the isEnum2 using for..in loop if you are using ES2017 or higher using Object.values:

return Object.values(Enum2).indexOf(value) > -1;

try it (Doesn't work in www.typescriptlang.org)

More info about Type Guards

share|improve this answer

answered Mar 27 at 10:33

AlbertoFdzMAlbertoFdzM

64688 silver badges2121 bronze badges

enum Enum1 
 N = 0,
 A = 1,
 B = 2


enum Enum2 
 A = 1,
 B = 2


interface Type1 
 a: Enum1;


interface Type2 
 a: Enum2;


const type1: Type1 = 
 a: Enum1.N
;

function isEnum2(value: any): value is Enum2 
 let isEnum2 = false;

 for (let key in Enum2) 
 if (Enum2[key] === value) 
 isEnum2 = true;
 
 

 return isEnum2;


if (isEnum2(type1.a)) 
 const type2: Type2 = 
 a: type1.a
 ;

return Object.values(Enum2).indexOf(value) > -1;

share|improve this answer

answered Mar 27 at 10:33

AlbertoFdzMAlbertoFdzM

64688 silver badges2121 bronze badges

answered Mar 27 at 10:33

AlbertoFdzMAlbertoFdzM

64688 silver badges2121 bronze badges

answered Mar 27 at 10:33

AlbertoFdzMAlbertoFdzM

64688 silver badges2121 bronze badges