Flow•3y ago

Downcasting from AnyResource?

Trying to figure out a way to allow for generic attachments to NFTs. Does anyone know if we can downcast from &ref as auth &AnyResource ? Something like

let myType: @MyType <- createMyType()
let attachments: @{Type: AnyResource} <- {Type<@MyType>(): myType}

let ref = (&attachments[tag] as auth &AnyResource?)!
let castedRef = ref as &MyType

let myType: @MyType <- createMyType()
let attachments: @{Type: AnyResource} <- {Type<@MyType>(): myType}

let ref = (&attachments[tag] as auth &AnyResource?)!
let castedRef = ref as &MyType

2 Replies

turbolent•3y ago

Yes, that is possible, as the reference is an authorized reference, which makes it downcastable. You just need to use a conditional cast (as?) or force-cast (as!), instead of a type assertion (as). as is a static check – statically, &AnyResource is not a subtype of &MyType . What you want to do is ref and try to cast it at run-time. Here's an example Playground: https://play.flow.com/83473238-9b05-4132-8464-ef210e300e0d?type=script&id=26f962de-3256-434f-8300-b28e6eccb190&storage=none

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Giovanni SOP•3y ago

Very helpful, thanks for the example!

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Downcasting from AnyResource?