Mixing
How to extend the Error interface with generic strings in Flow?
When I try to extend the Error interface in Flow to make the name property mandatory, Flow doesn't recognise my generic types as strings despite explicitly describing them as strings.
When I write that:
interface CustomError<A: string, B: string> extends Error {
message: A;
name: B;
}
I get these 2 (same) errors:
- Cannot extend
Error1 withCustomErrorbecauseA[2] is incompatible with string [3] in propertymessage. - Cannot extend
Error1 withCustomErrorbecauseB[2] is incompatible with string [3] in propertyname.
What's strange is that it tells me because A [2] is incompatible when A should be described as a string right away...
flowtype
asked Nov 19 '18 at 1:53
Edouard HienrichsEdouard Hienrichs
38211
add a comment |
When I try to extend the Error interface in Flow to make the name property mandatory, Flow doesn't recognise my generic types as strings despite explicitly describing them as strings.
When I write that:
interface CustomError<A: string, B: string> extends Error {
message: A;
name: B;
}
I get these 2 (same) errors:
- Cannot extend
Error1 withCustomErrorbecauseA[2] is incompatible with string [3] in propertymessage. - Cannot extend
Error1 withCustomErrorbecauseB[2] is incompatible with string [3] in propertyname.
What's strange is that it tells me because A [2] is incompatible when A should be described as a string right away...
flowtype
asked Nov 19 '18 at 1:53
Edouard HienrichsEdouard Hienrichs
38211
Why do you need to changeErrorbasic members type:messageandname? What you plan to put there beside the string?
– Alex
Nov 22 '18 at 8:34
1
@Alex I actually tried to isolate my issue. Not only I added other properties in my original code but the goal here is to make thename, which is natively not a mandatory property, a mandatory one. As for why I need it to be generic: this allows autocompletion to "show" the related strings since there is an error dictionary in the form of a string map object linked to these generic types.
– Edouard Hienrichs
Nov 22 '18 at 8:43
add a comment |
When I try to extend the Error interface in Flow to make the name property mandatory, Flow doesn't recognise my generic types as strings despite explicitly describing them as strings.
When I write that:
interface CustomError<A: string, B: string> extends Error {
message: A;
name: B;
}
I get these 2 (same) errors:
- Cannot extend
Error1 withCustomErrorbecauseA[2] is incompatible with string [3] in propertymessage. - Cannot extend
Error1 withCustomErrorbecauseB[2] is incompatible with string [3] in propertyname.
What's strange is that it tells me because A [2] is incompatible when A should be described as a string right away...
flowtype
asked Nov 19 '18 at 1:53
Edouard HienrichsEdouard Hienrichs
38211
When I try to extend the Error interface in Flow to make the name property mandatory, Flow doesn't recognise my generic types as strings despite explicitly describing them as strings.
When I write that:
interface CustomError<A: string, B: string> extends Error {
message: A;
name: B;
}
I get these 2 (same) errors:
- Cannot extend
Error1 withCustomErrorbecauseA[2] is incompatible with string [3] in propertymessage. - Cannot extend
Error1 withCustomErrorbecauseB[2] is incompatible with string [3] in propertyname.
What's strange is that it tells me because A [2] is incompatible when A should be described as a string right away...
flowtype
flowtype
asked Nov 19 '18 at 1:53
Edouard HienrichsEdouard Hienrichs
38211
asked Nov 19 '18 at 1:53
Edouard HienrichsEdouard Hienrichs
38211
edited Nov 21 '18 at 6:51
Edouard Hienrichs
asked Nov 19 '18 at 1:53
Edouard HienrichsEdouard Hienrichs
38211
asked Nov 19 '18 at 1:53
Edouard HienrichsEdouard Hienrichs
38211
asked Nov 19 '18 at 1:53
Edouard HienrichsEdouard Hienrichs
38211
38211
Why do you need to changeErrorbasic members type:messageandname? What you plan to put there beside the string?
– Alex
Nov 22 '18 at 8:34
1
@Alex I actually tried to isolate my issue. Not only I added other properties in my original code but the goal here is to make thename, which is natively not a mandatory property, a mandatory one. As for why I need it to be generic: this allows autocompletion to "show" the related strings since there is an error dictionary in the form of a string map object linked to these generic types.
– Edouard Hienrichs
Nov 22 '18 at 8:43
add a comment |
Why do you need to changeErrorbasic members type:messageandname? What you plan to put there beside the string?
– Alex
Nov 22 '18 at 8:34
1
@Alex I actually tried to isolate my issue. Not only I added other properties in my original code but the goal here is to make thename, which is natively not a mandatory property, a mandatory one. As for why I need it to be generic: this allows autocompletion to "show" the related strings since there is an error dictionary in the form of a string map object linked to these generic types.
– Edouard Hienrichs
Nov 22 '18 at 8:43
Why do you need to change
Error basic members type: message and name? What you plan to put there beside the string?– Alex
Nov 22 '18 at 8:34
Why do you need to change
Error basic members type: message and name? What you plan to put there beside the string?– Alex
Nov 22 '18 at 8:34
1
1
@Alex I actually tried to isolate my issue. Not only I added other properties in my original code but the goal here is to make the
name, which is natively not a mandatory property, a mandatory one. As for why I need it to be generic: this allows autocompletion to "show" the related strings since there is an error dictionary in the form of a string map object linked to these generic types.– Edouard Hienrichs
Nov 22 '18 at 8:43
@Alex I actually tried to isolate my issue. Not only I added other properties in my original code but the goal here is to make the
name, which is natively not a mandatory property, a mandatory one. As for why I need it to be generic: this allows autocompletion to "show" the related strings since there is an error dictionary in the form of a string map object linked to these generic types.– Edouard Hienrichs
Nov 22 '18 at 8:43
add a comment |
1 Answer
1
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votes
It's also not clear for me why it doesn't work, however something like this seems to be ok:
class CustomError<A: string, B: string> extends Error {
constructor(name: A, message: B) {
super(name);
this.name = name;
this.message = message;
}
}
type A = 'A' | 'A1';
type B = 'B' | 'B1';
class SpecificError extends CustomError<A, B> {}
//throw new SpecificError('a', 'c'); //error, wrong argument
throw new SpecificError('A', 'B'); //ok
Also, would note that js allows to throw any expression, not only Error children, so you might not need to extend Error class.
answered Nov 23 '18 at 1:47
AlexAlex
3,335621
add a comment |
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1 Answer
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active
oldest
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1 Answer
1
active
oldest
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active
oldest
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active
oldest
votes
It's also not clear for me why it doesn't work, however something like this seems to be ok:
class CustomError<A: string, B: string> extends Error {
constructor(name: A, message: B) {
super(name);
this.name = name;
this.message = message;
}
}
type A = 'A' | 'A1';
type B = 'B' | 'B1';
class SpecificError extends CustomError<A, B> {}
//throw new SpecificError('a', 'c'); //error, wrong argument
throw new SpecificError('A', 'B'); //ok
Also, would note that js allows to throw any expression, not only Error children, so you might not need to extend Error class.
answered Nov 23 '18 at 1:47
AlexAlex
3,335621
add a comment |
It's also not clear for me why it doesn't work, however something like this seems to be ok:
class CustomError<A: string, B: string> extends Error {
constructor(name: A, message: B) {
super(name);
this.name = name;
this.message = message;
}
}
type A = 'A' | 'A1';
type B = 'B' | 'B1';
class SpecificError extends CustomError<A, B> {}
//throw new SpecificError('a', 'c'); //error, wrong argument
throw new SpecificError('A', 'B'); //ok
Also, would note that js allows to throw any expression, not only Error children, so you might not need to extend Error class.
answered Nov 23 '18 at 1:47
AlexAlex
3,335621
add a comment |
It's also not clear for me why it doesn't work, however something like this seems to be ok:
class CustomError<A: string, B: string> extends Error {
constructor(name: A, message: B) {
super(name);
this.name = name;
this.message = message;
}
}
type A = 'A' | 'A1';
type B = 'B' | 'B1';
class SpecificError extends CustomError<A, B> {}
//throw new SpecificError('a', 'c'); //error, wrong argument
throw new SpecificError('A', 'B'); //ok
Also, would note that js allows to throw any expression, not only Error children, so you might not need to extend Error class.
answered Nov 23 '18 at 1:47
AlexAlex
3,335621
It's also not clear for me why it doesn't work, however something like this seems to be ok:
class CustomError<A: string, B: string> extends Error {
constructor(name: A, message: B) {
super(name);
this.name = name;
this.message = message;
}
}
type A = 'A' | 'A1';
type B = 'B' | 'B1';
class SpecificError extends CustomError<A, B> {}
//throw new SpecificError('a', 'c'); //error, wrong argument
throw new SpecificError('A', 'B'); //ok
Also, would note that js allows to throw any expression, not only Error children, so you might not need to extend Error class.
answered Nov 23 '18 at 1:47
AlexAlex
3,335621
answered Nov 23 '18 at 1:47
AlexAlex
3,335621
answered Nov 23 '18 at 1:47
AlexAlex
3,335621
answered Nov 23 '18 at 1:47
AlexAlex
3,335621
3,335621
add a comment |
add a comment |
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Why do you need to change
Errorbasic members type:messageandname? What you plan to put there beside the string?– Alex
Nov 22 '18 at 8:34
1
@Alex I actually tried to isolate my issue. Not only I added other properties in my original code but the goal here is to make the
name, which is natively not a mandatory property, a mandatory one. As for why I need it to be generic: this allows autocompletion to "show" the related strings since there is an error dictionary in the form of a string map object linked to these generic types.– Edouard Hienrichs
Nov 22 '18 at 8:43