Typescript Generic Promise Return Type
1
Basically I'm trying to implement a function that always returns a fulfilled promise of the same "type" i pass to the function as a parameter
So if I call with a boolean it returns a fulfilled Promise, if I call with a string parameter it returns a fulfilled Promise and so on..
what I tried so far:
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
I don't know if it's the proper way to do it and in any case it breaks if i try to get a Promise< void >
Any suggestion will be appreciated
typescript generics promise typescript-generics
asked Nov 23 '18 at 11:00
PlasticPlastic
1,94521632
add a comment |
1
Basically I'm trying to implement a function that always returns a fulfilled promise of the same "type" i pass to the function as a parameter
So if I call with a boolean it returns a fulfilled Promise, if I call with a string parameter it returns a fulfilled Promise and so on..
what I tried so far:
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
I don't know if it's the proper way to do it and in any case it breaks if i try to get a Promise< void >
Any suggestion will be appreciated
typescript generics promise typescript-generics
asked Nov 23 '18 at 11:00
PlasticPlastic
1,94521632
add a comment |
1
1
1
1
Basically I'm trying to implement a function that always returns a fulfilled promise of the same "type" i pass to the function as a parameter
So if I call with a boolean it returns a fulfilled Promise, if I call with a string parameter it returns a fulfilled Promise and so on..
what I tried so far:
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
I don't know if it's the proper way to do it and in any case it breaks if i try to get a Promise< void >
Any suggestion will be appreciated
typescript generics promise typescript-generics
asked Nov 23 '18 at 11:00
PlasticPlastic
1,94521632
Basically I'm trying to implement a function that always returns a fulfilled promise of the same "type" i pass to the function as a parameter
So if I call with a boolean it returns a fulfilled Promise, if I call with a string parameter it returns a fulfilled Promise and so on..
what I tried so far:
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
I don't know if it's the proper way to do it and in any case it breaks if i try to get a Promise< void >
Any suggestion will be appreciated
typescript generics promise typescript-generics
typescript generics promise typescript-generics
asked Nov 23 '18 at 11:00
PlasticPlastic
1,94521632
asked Nov 23 '18 at 11:00
PlasticPlastic
1,94521632
asked Nov 23 '18 at 11:00
PlasticPlastic
1,94521632
asked Nov 23 '18 at 11:00
PlasticPlastic
1,94521632
asked Nov 23 '18 at 11:00
PlasticPlastic
1,94521632
1,94521632
add a comment |
add a comment |
2 Answers
2
active
oldest
votes
2
You implementation seems fine, the problem with void is that the parameter is still expected. You could call it with undefined
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
PromiseOK<void>(undefined)
A better option might be to use overloads to get special behavior for void:
function PromiseOK(): Promise<void>
function PromiseOK<T>(val: T): Promise<T>
function PromiseOK<T>(val?: T): Promise<T> {
return Promise.resolve(val);
};
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
It is possible to have overloads with arrow functions, but the syntax is not exactly pretty :
const PromiseOK: {
(): Promise<void>
<T>(val: T): Promise<T>
} = <T>(val?: T): Promise<T> => Promise.resolve(val);
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
answered Nov 23 '18 at 11:42
Titian Cernicova-DragomirTitian Cernicova-Dragomir
72.1k35068
Thanks a lot, I like the idea of using overloads, is it possible to use overloads with the arrow notation?
– Plastic
Nov 23 '18 at 11:48
@Plastic yes yo can (edited the answer), but the syntax is not exactly great ... I would stick with regular functions for overloads if you don't need the capturethisbehavior
– Titian Cernicova-Dragomir
Nov 23 '18 at 11:53
@TitianCernicova-Dragomir Hi, I am wondering if it possible to use the generic type in the function? Likepublic promiseOK<T>(endpoint: string, returnType: T): Promise<T> { const promise: Promise<returnType>...returnType is unknown here.cannot find name returnType. I am trying to make a generic wrapper-function. How can I make Promise take it as an argument?
– Joel
Feb 8 at 10:13
@Joel the type parameter represents the type ofreturnTypeyou should use that :Promise<T>will work fine in the body of the function.
– Titian Cernicova-Dragomir
Feb 8 at 10:15
@TitianCernicova-Dragomir I have asked a question recently where I am explaining a bit more what I am after. Do you mind taking a look? Thanks.
– Joel
Feb 8 at 10:16
add a comment |
0
It should look like this
function PromiseOK<T>(val: T): Promise<T> {
return Promise.resolve(val);
};
If you want to keep the fat arrow notation, then
const PromiseOK = <T extends any>(val: T): Promise<T> => {
return Promise.resolve(val);
};
The notation T extends any also supports void.
answered Nov 23 '18 at 11:07
Murat KaragözMurat Karagöz
15.4k53771
thanks for the answer, the thing is if i try to call asPromiseOK()the compiler says that the function expect one argument... it could be solved givingvalas a optional parameter??
– Plastic
Nov 23 '18 at 11:17
@Plastic Yes, it can be solved like that. But then the function would make no sense?
– Murat Karagöz
Nov 23 '18 at 11:51
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
2
You implementation seems fine, the problem with void is that the parameter is still expected. You could call it with undefined
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
PromiseOK<void>(undefined)
A better option might be to use overloads to get special behavior for void:
function PromiseOK(): Promise<void>
function PromiseOK<T>(val: T): Promise<T>
function PromiseOK<T>(val?: T): Promise<T> {
return Promise.resolve(val);
};
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
It is possible to have overloads with arrow functions, but the syntax is not exactly pretty :
const PromiseOK: {
(): Promise<void>
<T>(val: T): Promise<T>
} = <T>(val?: T): Promise<T> => Promise.resolve(val);
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
answered Nov 23 '18 at 11:42
Titian Cernicova-DragomirTitian Cernicova-Dragomir
72.1k35068
Thanks a lot, I like the idea of using overloads, is it possible to use overloads with the arrow notation?
– Plastic
Nov 23 '18 at 11:48
@Plastic yes yo can (edited the answer), but the syntax is not exactly great ... I would stick with regular functions for overloads if you don't need the capturethisbehavior
– Titian Cernicova-Dragomir
Nov 23 '18 at 11:53
@TitianCernicova-Dragomir Hi, I am wondering if it possible to use the generic type in the function? Likepublic promiseOK<T>(endpoint: string, returnType: T): Promise<T> { const promise: Promise<returnType>...returnType is unknown here.cannot find name returnType. I am trying to make a generic wrapper-function. How can I make Promise take it as an argument?
– Joel
Feb 8 at 10:13
@Joel the type parameter represents the type ofreturnTypeyou should use that :Promise<T>will work fine in the body of the function.
– Titian Cernicova-Dragomir
Feb 8 at 10:15
@TitianCernicova-Dragomir I have asked a question recently where I am explaining a bit more what I am after. Do you mind taking a look? Thanks.
– Joel
Feb 8 at 10:16
add a comment |
2
You implementation seems fine, the problem with void is that the parameter is still expected. You could call it with undefined
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
PromiseOK<void>(undefined)
A better option might be to use overloads to get special behavior for void:
function PromiseOK(): Promise<void>
function PromiseOK<T>(val: T): Promise<T>
function PromiseOK<T>(val?: T): Promise<T> {
return Promise.resolve(val);
};
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
It is possible to have overloads with arrow functions, but the syntax is not exactly pretty :
const PromiseOK: {
(): Promise<void>
<T>(val: T): Promise<T>
} = <T>(val?: T): Promise<T> => Promise.resolve(val);
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
answered Nov 23 '18 at 11:42
Titian Cernicova-DragomirTitian Cernicova-Dragomir
72.1k35068
Thanks a lot, I like the idea of using overloads, is it possible to use overloads with the arrow notation?
– Plastic
Nov 23 '18 at 11:48
@Plastic yes yo can (edited the answer), but the syntax is not exactly great ... I would stick with regular functions for overloads if you don't need the capturethisbehavior
– Titian Cernicova-Dragomir
Nov 23 '18 at 11:53
@TitianCernicova-Dragomir Hi, I am wondering if it possible to use the generic type in the function? Likepublic promiseOK<T>(endpoint: string, returnType: T): Promise<T> { const promise: Promise<returnType>...returnType is unknown here.cannot find name returnType. I am trying to make a generic wrapper-function. How can I make Promise take it as an argument?
– Joel
Feb 8 at 10:13
@Joel the type parameter represents the type ofreturnTypeyou should use that :Promise<T>will work fine in the body of the function.
– Titian Cernicova-Dragomir
Feb 8 at 10:15
@TitianCernicova-Dragomir I have asked a question recently where I am explaining a bit more what I am after. Do you mind taking a look? Thanks.
– Joel
Feb 8 at 10:16
add a comment |
2
2
2
You implementation seems fine, the problem with void is that the parameter is still expected. You could call it with undefined
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
PromiseOK<void>(undefined)
A better option might be to use overloads to get special behavior for void:
function PromiseOK(): Promise<void>
function PromiseOK<T>(val: T): Promise<T>
function PromiseOK<T>(val?: T): Promise<T> {
return Promise.resolve(val);
};
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
It is possible to have overloads with arrow functions, but the syntax is not exactly pretty :
const PromiseOK: {
(): Promise<void>
<T>(val: T): Promise<T>
} = <T>(val?: T): Promise<T> => Promise.resolve(val);
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
answered Nov 23 '18 at 11:42
Titian Cernicova-DragomirTitian Cernicova-Dragomir
72.1k35068
You implementation seems fine, the problem with void is that the parameter is still expected. You could call it with undefined
const PromiseOK = <T>(val: T): Promise<T> => {
return Promise.resolve(val);
};
PromiseOK<void>(undefined)
A better option might be to use overloads to get special behavior for void:
function PromiseOK(): Promise<void>
function PromiseOK<T>(val: T): Promise<T>
function PromiseOK<T>(val?: T): Promise<T> {
return Promise.resolve(val);
};
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
It is possible to have overloads with arrow functions, but the syntax is not exactly pretty :
const PromiseOK: {
(): Promise<void>
<T>(val: T): Promise<T>
} = <T>(val?: T): Promise<T> => Promise.resolve(val);
PromiseOK() // Promise<void>
PromiseOK(1) //Promise<number>
answered Nov 23 '18 at 11:42
Titian Cernicova-DragomirTitian Cernicova-Dragomir
72.1k35068
edited Nov 23 '18 at 11:52
answered Nov 23 '18 at 11:42
Titian Cernicova-DragomirTitian Cernicova-Dragomir
72.1k35068
answered Nov 23 '18 at 11:42
Titian Cernicova-DragomirTitian Cernicova-Dragomir
72.1k35068
answered Nov 23 '18 at 11:42
Titian Cernicova-DragomirTitian Cernicova-Dragomir
72.1k35068
72.1k35068
Thanks a lot, I like the idea of using overloads, is it possible to use overloads with the arrow notation?
– Plastic
Nov 23 '18 at 11:48
@Plastic yes yo can (edited the answer), but the syntax is not exactly great ... I would stick with regular functions for overloads if you don't need the capturethisbehavior
– Titian Cernicova-Dragomir
Nov 23 '18 at 11:53
@TitianCernicova-Dragomir Hi, I am wondering if it possible to use the generic type in the function? Likepublic promiseOK<T>(endpoint: string, returnType: T): Promise<T> { const promise: Promise<returnType>...returnType is unknown here.cannot find name returnType. I am trying to make a generic wrapper-function. How can I make Promise take it as an argument?
– Joel
Feb 8 at 10:13
@Joel the type parameter represents the type ofreturnTypeyou should use that :Promise<T>will work fine in the body of the function.
– Titian Cernicova-Dragomir
Feb 8 at 10:15
@TitianCernicova-Dragomir I have asked a question recently where I am explaining a bit more what I am after. Do you mind taking a look? Thanks.
– Joel
Feb 8 at 10:16
add a comment |
Thanks a lot, I like the idea of using overloads, is it possible to use overloads with the arrow notation?
– Plastic
Nov 23 '18 at 11:48
@Plastic yes yo can (edited the answer), but the syntax is not exactly great ... I would stick with regular functions for overloads if you don't need the capturethisbehavior
– Titian Cernicova-Dragomir
Nov 23 '18 at 11:53
@TitianCernicova-Dragomir Hi, I am wondering if it possible to use the generic type in the function? Likepublic promiseOK<T>(endpoint: string, returnType: T): Promise<T> { const promise: Promise<returnType>...returnType is unknown here.cannot find name returnType. I am trying to make a generic wrapper-function. How can I make Promise take it as an argument?
– Joel
Feb 8 at 10:13
@Joel the type parameter represents the type ofreturnTypeyou should use that :Promise<T>will work fine in the body of the function.
– Titian Cernicova-Dragomir
Feb 8 at 10:15
@TitianCernicova-Dragomir I have asked a question recently where I am explaining a bit more what I am after. Do you mind taking a look? Thanks.
– Joel
Feb 8 at 10:16
Thanks a lot, I like the idea of using overloads, is it possible to use overloads with the arrow notation?
– Plastic
Nov 23 '18 at 11:48
Thanks a lot, I like the idea of using overloads, is it possible to use overloads with the arrow notation?
– Plastic
Nov 23 '18 at 11:48
@Plastic yes yo can (edited the answer), but the syntax is not exactly great ... I would stick with regular functions for overloads if you don't need the capture
this behavior– Titian Cernicova-Dragomir
Nov 23 '18 at 11:53
@Plastic yes yo can (edited the answer), but the syntax is not exactly great ... I would stick with regular functions for overloads if you don't need the capture
this behavior– Titian Cernicova-Dragomir
Nov 23 '18 at 11:53
@TitianCernicova-Dragomir Hi, I am wondering if it possible to use the generic type in the function? Like
public promiseOK<T>(endpoint: string, returnType: T): Promise<T> { const promise: Promise<returnType>... returnType is unknown here. cannot find name returnType. I am trying to make a generic wrapper-function. How can I make Promise take it as an argument?– Joel
Feb 8 at 10:13
@TitianCernicova-Dragomir Hi, I am wondering if it possible to use the generic type in the function? Like
public promiseOK<T>(endpoint: string, returnType: T): Promise<T> { const promise: Promise<returnType>... returnType is unknown here. cannot find name returnType. I am trying to make a generic wrapper-function. How can I make Promise take it as an argument?– Joel
Feb 8 at 10:13
@Joel the type parameter represents the type of
returnType you should use that : Promise<T> will work fine in the body of the function.– Titian Cernicova-Dragomir
Feb 8 at 10:15
@Joel the type parameter represents the type of
returnType you should use that : Promise<T> will work fine in the body of the function.– Titian Cernicova-Dragomir
Feb 8 at 10:15
@TitianCernicova-Dragomir I have asked a question recently where I am explaining a bit more what I am after. Do you mind taking a look? Thanks.
– Joel
Feb 8 at 10:16
@TitianCernicova-Dragomir I have asked a question recently where I am explaining a bit more what I am after. Do you mind taking a look? Thanks.
– Joel
Feb 8 at 10:16
add a comment |
0
It should look like this
function PromiseOK<T>(val: T): Promise<T> {
return Promise.resolve(val);
};
If you want to keep the fat arrow notation, then
const PromiseOK = <T extends any>(val: T): Promise<T> => {
return Promise.resolve(val);
};
The notation T extends any also supports void.
answered Nov 23 '18 at 11:07
Murat KaragözMurat Karagöz
15.4k53771
thanks for the answer, the thing is if i try to call asPromiseOK()the compiler says that the function expect one argument... it could be solved givingvalas a optional parameter??
– Plastic
Nov 23 '18 at 11:17
@Plastic Yes, it can be solved like that. But then the function would make no sense?
– Murat Karagöz
Nov 23 '18 at 11:51
add a comment |
0
It should look like this
function PromiseOK<T>(val: T): Promise<T> {
return Promise.resolve(val);
};
If you want to keep the fat arrow notation, then
const PromiseOK = <T extends any>(val: T): Promise<T> => {
return Promise.resolve(val);
};
The notation T extends any also supports void.
answered Nov 23 '18 at 11:07
Murat KaragözMurat Karagöz
15.4k53771
thanks for the answer, the thing is if i try to call asPromiseOK()the compiler says that the function expect one argument... it could be solved givingvalas a optional parameter??
– Plastic
Nov 23 '18 at 11:17
@Plastic Yes, it can be solved like that. But then the function would make no sense?
– Murat Karagöz
Nov 23 '18 at 11:51
add a comment |
0
0
0
It should look like this
function PromiseOK<T>(val: T): Promise<T> {
return Promise.resolve(val);
};
If you want to keep the fat arrow notation, then
const PromiseOK = <T extends any>(val: T): Promise<T> => {
return Promise.resolve(val);
};
The notation T extends any also supports void.
answered Nov 23 '18 at 11:07
Murat KaragözMurat Karagöz
15.4k53771
It should look like this
function PromiseOK<T>(val: T): Promise<T> {
return Promise.resolve(val);
};
If you want to keep the fat arrow notation, then
const PromiseOK = <T extends any>(val: T): Promise<T> => {
return Promise.resolve(val);
};
The notation T extends any also supports void.
answered Nov 23 '18 at 11:07
Murat KaragözMurat Karagöz
15.4k53771
answered Nov 23 '18 at 11:07
Murat KaragözMurat Karagöz
15.4k53771
answered Nov 23 '18 at 11:07
Murat KaragözMurat Karagöz
15.4k53771
answered Nov 23 '18 at 11:07
Murat KaragözMurat Karagöz
15.4k53771
15.4k53771
thanks for the answer, the thing is if i try to call asPromiseOK()the compiler says that the function expect one argument... it could be solved givingvalas a optional parameter??
– Plastic
Nov 23 '18 at 11:17
@Plastic Yes, it can be solved like that. But then the function would make no sense?
– Murat Karagöz
Nov 23 '18 at 11:51
add a comment |
thanks for the answer, the thing is if i try to call asPromiseOK()the compiler says that the function expect one argument... it could be solved givingvalas a optional parameter??
– Plastic
Nov 23 '18 at 11:17
@Plastic Yes, it can be solved like that. But then the function would make no sense?
– Murat Karagöz
Nov 23 '18 at 11:51
thanks for the answer, the thing is if i try to call as
PromiseOK() the compiler says that the function expect one argument... it could be solved giving val as a optional parameter??– Plastic
Nov 23 '18 at 11:17
thanks for the answer, the thing is if i try to call as
PromiseOK() the compiler says that the function expect one argument... it could be solved giving val as a optional parameter??– Plastic
Nov 23 '18 at 11:17
@Plastic Yes, it can be solved like that. But then the function would make no sense?
– Murat Karagöz
Nov 23 '18 at 11:51
@Plastic Yes, it can be solved like that. But then the function would make no sense?
– Murat Karagöz
Nov 23 '18 at 11:51
add a comment |
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