type-extension | 易学教程

Typescript Declaration Merging fail about Express Request

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问题 When i extend express request, i got this erorr. error TS2339: Property 'test' does not exist on type 'Request<ParamsDictionary, any, any, ParsedQs>'. This is my test code that extend request. app.get('/auth/google/callback', passport.authenticate('google', { failureRedirect: '/login' }), function(req: Request, res: Response) { req.test = 'aa' return console.log(req.test) }); For solving it, i already searched a lot and i did it. Make types/express/index.d.ts file. i add typeRoots in tsconfig

Typescript Declaration Merging fail about Express Request

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F# generating types in a type extension function within a type provider

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问题 I have the following problem: Within my type provider, I need to extend a generic type, that I have previously defined, with a method that will return an instance of this generic type. What I mean is, let's say we have : type receiveType<'a> = class val Next:int val Type:string new (state,stateType) = {Next = state;Type = stateType;} end later within my typeprovider I want to extend the type with the following function: [<TypeProvider>] type ProviderTest() as this= ( inherit

Extension method with F# function type

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问题 The MSDN doc on Type Extensions states that "Before F# 3.1, the F# compiler didn't support the use of C#-style extension methods with a generic type variable, array type, tuple type, or an F# function type as the “this” parameter." (http://msdn.microsoft.com/en-us/library/dd233211.aspx) How can be a Type Extension used on F# function type? In what situations would such a feature be useful? 回答1: Here is how you can do it: [<Extension>] type FunctionExtension() = [<Extension>] static member

F# how to extended the generic array type? [duplicate]

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问题 This question already has answers here : How to define a type extension for T[] in F#? (2 answers) Closed 6 years ago . Following this question I wonder how (or if) i can extend the generic F# Array Type. I could do this: type System.Array with member a.Last = a.GetValue(a.Length - 1) but as Tomas mentioned it is non generic. Next I tried this but it does not work: type Microsoft.FSharp.Collections.Array with // Error: Array is not defined member a.Last = a.[a.Length - 1] In the F# scource I

Scoped type variables require explicit foralls. Why?

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问题 If you want to use GHC's lexically scoped type variables, you also have to use explicit universal quantification. That is, you have to add forall declarations to your functions' type signatures: {-# LANGUAGE ExplicitForAll, ScopedTypeVariables #-} f :: forall a . [a] -> [a] -- The `forall` is required here ... f (x:xs) = xs ++ [x :: a] -- ... to relate this `a` to the ones above. Does this actually have anything to do with quantification, or did the extension writers just coopt the forall

Fun with types! Resolving multiple instance declarations

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问题 I'm trying to write some Haskell code in which there are multiple data types, each of which can have multiple implementations. To do this, I define each data type as a class whose methods are the relevant constructors and selectors, and then implement all operations on members of that class in terms of the given constructors and selectors. For example, perhaps A is a polynomial class (with methods getCoefficients and makePolynomial ) which can have a representation as a SparsePoly or a

Fun with types! Resolving multiple instance declarations

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I'm trying to write some Haskell code in which there are multiple data types, each of which can have multiple implementations. To do this, I define each data type as a class whose methods are the relevant constructors and selectors, and then implement all operations on members of that class in terms of the given constructors and selectors. For example, perhaps A is a polynomial class (with methods getCoefficients and makePolynomial ) which can have a representation as a SparsePoly or a DensePoly and B is a complex number class (with methods getReal , getImag and makeComplex ) which can be