Unboxing Instances of Different Types with a Generic Type Parameter that Implements an Interface
I am working on an abstraction for a variation on a key-value store style API where I have the following interfaces (simplified for clarity).
type IValue =
abstract member Id: int64
type IKey<'value when 'value :> IValue> = interface end
type IKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
type IKeyValueStore<'value when 'value :> IValue> =
abstract member Store: 'value -> unit
abstract member Get: int64 -> 'value option
abstract member Find<'key when 'key :> IKey<'value>> : 'key -> 'value option
Basically, each value can be looked up by multiple keys, and the keys for each value are generated by IKeyGenerator
s. When I call Store
on the IKeyValueStore
, I want to find all the key generators for the given value, run each of them, and store each key for the value so it can then be retrieved by any of those keys.
My problem is that, while I can reflectively discover all implementations of IKeyGenerator
that have a 'value
type parameter that matches the 'value
type for this IKeyValueStore
, I can't safely unbox them to a consistent type. I tried unboxing them all to IKeyGenerator<'value, IKey<'value>>
, but this doesn't work if the concrete implementations don't explicitly implement the interface that way. If they implement the interface referring to a specific implementation of IKey
, the unboxing fails.
I then tried introducing a simplified IKeyGenerator<'value>
interface that defined the Generate
method as simply returning IKey<'value>
instead of 'key :> IKey<'value>
, which solves the problem with unboxing all the implementations, but I then run into problems downstream with not knowing the actual type of the key (for example, in order to do the Find
when there are multiple possible keys for this value).
Is there some way I can safely obtain a list of IKeyGenerator
instances for different IKey
implementations, provided that they all implement IKey<'value>
for the same type of value?
.net generics f#
add a comment |
I am working on an abstraction for a variation on a key-value store style API where I have the following interfaces (simplified for clarity).
type IValue =
abstract member Id: int64
type IKey<'value when 'value :> IValue> = interface end
type IKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
type IKeyValueStore<'value when 'value :> IValue> =
abstract member Store: 'value -> unit
abstract member Get: int64 -> 'value option
abstract member Find<'key when 'key :> IKey<'value>> : 'key -> 'value option
Basically, each value can be looked up by multiple keys, and the keys for each value are generated by IKeyGenerator
s. When I call Store
on the IKeyValueStore
, I want to find all the key generators for the given value, run each of them, and store each key for the value so it can then be retrieved by any of those keys.
My problem is that, while I can reflectively discover all implementations of IKeyGenerator
that have a 'value
type parameter that matches the 'value
type for this IKeyValueStore
, I can't safely unbox them to a consistent type. I tried unboxing them all to IKeyGenerator<'value, IKey<'value>>
, but this doesn't work if the concrete implementations don't explicitly implement the interface that way. If they implement the interface referring to a specific implementation of IKey
, the unboxing fails.
I then tried introducing a simplified IKeyGenerator<'value>
interface that defined the Generate
method as simply returning IKey<'value>
instead of 'key :> IKey<'value>
, which solves the problem with unboxing all the implementations, but I then run into problems downstream with not knowing the actual type of the key (for example, in order to do the Find
when there are multiple possible keys for this value).
Is there some way I can safely obtain a list of IKeyGenerator
instances for different IKey
implementations, provided that they all implement IKey<'value>
for the same type of value?
.net generics f#
add a comment |
I am working on an abstraction for a variation on a key-value store style API where I have the following interfaces (simplified for clarity).
type IValue =
abstract member Id: int64
type IKey<'value when 'value :> IValue> = interface end
type IKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
type IKeyValueStore<'value when 'value :> IValue> =
abstract member Store: 'value -> unit
abstract member Get: int64 -> 'value option
abstract member Find<'key when 'key :> IKey<'value>> : 'key -> 'value option
Basically, each value can be looked up by multiple keys, and the keys for each value are generated by IKeyGenerator
s. When I call Store
on the IKeyValueStore
, I want to find all the key generators for the given value, run each of them, and store each key for the value so it can then be retrieved by any of those keys.
My problem is that, while I can reflectively discover all implementations of IKeyGenerator
that have a 'value
type parameter that matches the 'value
type for this IKeyValueStore
, I can't safely unbox them to a consistent type. I tried unboxing them all to IKeyGenerator<'value, IKey<'value>>
, but this doesn't work if the concrete implementations don't explicitly implement the interface that way. If they implement the interface referring to a specific implementation of IKey
, the unboxing fails.
I then tried introducing a simplified IKeyGenerator<'value>
interface that defined the Generate
method as simply returning IKey<'value>
instead of 'key :> IKey<'value>
, which solves the problem with unboxing all the implementations, but I then run into problems downstream with not knowing the actual type of the key (for example, in order to do the Find
when there are multiple possible keys for this value).
Is there some way I can safely obtain a list of IKeyGenerator
instances for different IKey
implementations, provided that they all implement IKey<'value>
for the same type of value?
.net generics f#
I am working on an abstraction for a variation on a key-value store style API where I have the following interfaces (simplified for clarity).
type IValue =
abstract member Id: int64
type IKey<'value when 'value :> IValue> = interface end
type IKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
type IKeyValueStore<'value when 'value :> IValue> =
abstract member Store: 'value -> unit
abstract member Get: int64 -> 'value option
abstract member Find<'key when 'key :> IKey<'value>> : 'key -> 'value option
Basically, each value can be looked up by multiple keys, and the keys for each value are generated by IKeyGenerator
s. When I call Store
on the IKeyValueStore
, I want to find all the key generators for the given value, run each of them, and store each key for the value so it can then be retrieved by any of those keys.
My problem is that, while I can reflectively discover all implementations of IKeyGenerator
that have a 'value
type parameter that matches the 'value
type for this IKeyValueStore
, I can't safely unbox them to a consistent type. I tried unboxing them all to IKeyGenerator<'value, IKey<'value>>
, but this doesn't work if the concrete implementations don't explicitly implement the interface that way. If they implement the interface referring to a specific implementation of IKey
, the unboxing fails.
I then tried introducing a simplified IKeyGenerator<'value>
interface that defined the Generate
method as simply returning IKey<'value>
instead of 'key :> IKey<'value>
, which solves the problem with unboxing all the implementations, but I then run into problems downstream with not knowing the actual type of the key (for example, in order to do the Find
when there are multiple possible keys for this value).
Is there some way I can safely obtain a list of IKeyGenerator
instances for different IKey
implementations, provided that they all implement IKey<'value>
for the same type of value?
.net generics f#
.net generics f#
asked Nov 14 '18 at 15:33
Aaron M. EshbachAaron M. Eshbach
4,907918
4,907918
add a comment |
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1 Answer
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I would recommend a two-tier implementation of the key generators: a base class that implements IKeyGenerator
, but itself has more concrete type parameters, constrained in the way you have there:
type IKeyGenerator<'value when 'value :> IValue> =
abstract member Generate: 'value -> IKey<'value>
[<AbstractClass>]
type KeyGeneratorBase<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
interface IKeyGenerator<'value> with
override this.Generate v = this.Generate v :> _
Then have specific implementations inherit from KeyGeneratorBase
.
This way, the implementations can have their concrete types to work with, and the consumer will have the narrow types that it expects.
Or, alternatively (and I much prefer this way), have a function to create IKeyGenerator
s:
let mkKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> (gen : 'value -> 'key) =
new IKeyGenerator<_> with
member this.Generate v = gen v :> _
P.S. I know this is not what you asked for, but I must warn against excessive use of reflection and classes. This never ends well. Consider a more functional, idiomatic approach.
I ended up going with a variation of the second solution here, where I just tag a function of'value -> 'key
with an attribute and then do the interface generation dynamically when I find that attribute. I think this will satisfy my OO consumers while making it idiomatic for F# users as well.
– Aaron M. Eshbach
Nov 15 '18 at 16:42
add a comment |
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1 Answer
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1 Answer
1
active
oldest
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active
oldest
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active
oldest
votes
I would recommend a two-tier implementation of the key generators: a base class that implements IKeyGenerator
, but itself has more concrete type parameters, constrained in the way you have there:
type IKeyGenerator<'value when 'value :> IValue> =
abstract member Generate: 'value -> IKey<'value>
[<AbstractClass>]
type KeyGeneratorBase<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
interface IKeyGenerator<'value> with
override this.Generate v = this.Generate v :> _
Then have specific implementations inherit from KeyGeneratorBase
.
This way, the implementations can have their concrete types to work with, and the consumer will have the narrow types that it expects.
Or, alternatively (and I much prefer this way), have a function to create IKeyGenerator
s:
let mkKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> (gen : 'value -> 'key) =
new IKeyGenerator<_> with
member this.Generate v = gen v :> _
P.S. I know this is not what you asked for, but I must warn against excessive use of reflection and classes. This never ends well. Consider a more functional, idiomatic approach.
I ended up going with a variation of the second solution here, where I just tag a function of'value -> 'key
with an attribute and then do the interface generation dynamically when I find that attribute. I think this will satisfy my OO consumers while making it idiomatic for F# users as well.
– Aaron M. Eshbach
Nov 15 '18 at 16:42
add a comment |
I would recommend a two-tier implementation of the key generators: a base class that implements IKeyGenerator
, but itself has more concrete type parameters, constrained in the way you have there:
type IKeyGenerator<'value when 'value :> IValue> =
abstract member Generate: 'value -> IKey<'value>
[<AbstractClass>]
type KeyGeneratorBase<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
interface IKeyGenerator<'value> with
override this.Generate v = this.Generate v :> _
Then have specific implementations inherit from KeyGeneratorBase
.
This way, the implementations can have their concrete types to work with, and the consumer will have the narrow types that it expects.
Or, alternatively (and I much prefer this way), have a function to create IKeyGenerator
s:
let mkKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> (gen : 'value -> 'key) =
new IKeyGenerator<_> with
member this.Generate v = gen v :> _
P.S. I know this is not what you asked for, but I must warn against excessive use of reflection and classes. This never ends well. Consider a more functional, idiomatic approach.
I ended up going with a variation of the second solution here, where I just tag a function of'value -> 'key
with an attribute and then do the interface generation dynamically when I find that attribute. I think this will satisfy my OO consumers while making it idiomatic for F# users as well.
– Aaron M. Eshbach
Nov 15 '18 at 16:42
add a comment |
I would recommend a two-tier implementation of the key generators: a base class that implements IKeyGenerator
, but itself has more concrete type parameters, constrained in the way you have there:
type IKeyGenerator<'value when 'value :> IValue> =
abstract member Generate: 'value -> IKey<'value>
[<AbstractClass>]
type KeyGeneratorBase<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
interface IKeyGenerator<'value> with
override this.Generate v = this.Generate v :> _
Then have specific implementations inherit from KeyGeneratorBase
.
This way, the implementations can have their concrete types to work with, and the consumer will have the narrow types that it expects.
Or, alternatively (and I much prefer this way), have a function to create IKeyGenerator
s:
let mkKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> (gen : 'value -> 'key) =
new IKeyGenerator<_> with
member this.Generate v = gen v :> _
P.S. I know this is not what you asked for, but I must warn against excessive use of reflection and classes. This never ends well. Consider a more functional, idiomatic approach.
I would recommend a two-tier implementation of the key generators: a base class that implements IKeyGenerator
, but itself has more concrete type parameters, constrained in the way you have there:
type IKeyGenerator<'value when 'value :> IValue> =
abstract member Generate: 'value -> IKey<'value>
[<AbstractClass>]
type KeyGeneratorBase<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> =
abstract member Generate: 'value -> 'key
interface IKeyGenerator<'value> with
override this.Generate v = this.Generate v :> _
Then have specific implementations inherit from KeyGeneratorBase
.
This way, the implementations can have their concrete types to work with, and the consumer will have the narrow types that it expects.
Or, alternatively (and I much prefer this way), have a function to create IKeyGenerator
s:
let mkKeyGenerator<'value, 'key when 'value :> IValue and 'key :> IKey<'value>> (gen : 'value -> 'key) =
new IKeyGenerator<_> with
member this.Generate v = gen v :> _
P.S. I know this is not what you asked for, but I must warn against excessive use of reflection and classes. This never ends well. Consider a more functional, idiomatic approach.
edited Nov 14 '18 at 17:03
answered Nov 14 '18 at 16:49
Fyodor SoikinFyodor Soikin
42.9k56699
42.9k56699
I ended up going with a variation of the second solution here, where I just tag a function of'value -> 'key
with an attribute and then do the interface generation dynamically when I find that attribute. I think this will satisfy my OO consumers while making it idiomatic for F# users as well.
– Aaron M. Eshbach
Nov 15 '18 at 16:42
add a comment |
I ended up going with a variation of the second solution here, where I just tag a function of'value -> 'key
with an attribute and then do the interface generation dynamically when I find that attribute. I think this will satisfy my OO consumers while making it idiomatic for F# users as well.
– Aaron M. Eshbach
Nov 15 '18 at 16:42
I ended up going with a variation of the second solution here, where I just tag a function of
'value -> 'key
with an attribute and then do the interface generation dynamically when I find that attribute. I think this will satisfy my OO consumers while making it idiomatic for F# users as well.– Aaron M. Eshbach
Nov 15 '18 at 16:42
I ended up going with a variation of the second solution here, where I just tag a function of
'value -> 'key
with an attribute and then do the interface generation dynamically when I find that attribute. I think this will satisfy my OO consumers while making it idiomatic for F# users as well.– Aaron M. Eshbach
Nov 15 '18 at 16:42
add a comment |
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