CODEWITHSUNDEEP
genericsf#interopc#-to-f#
Mike S
Mike S

Reputation: 166

F# Interop with C# function that has generic return type

When I have a generic function in C#, where the generic argument defines the return type of the function only, F# seems incapable of infering the generic argument. I also do not know how to type-annotate this.

For example, the following C# function is very common in lightweight ORMs, such as dapper.net and ServiceStack-ORM-Lite:

public T Get<T>(string sql)
{
    //.... 
    var obj = Activator.CreateInstance<T>();
    //....
    return obj;
}

let say i try and use this in F#... firstly by type inference:

let GetCustomer sql : Customer = 
    MyCSharpObj.Get(sql)

Or, I try to annotate the type (not even sure if this syntax is correct):

let GetCustomer sql : Customer = 
    MyCSharpObj.Get<Customer>(sql)

In both instances, i get the compile error (on the MyCSharpObj.Get line):

Lookup on object of indeterminate type based on information prior to this program point. A type annotation may be needed prior to this program point to constrain the type of the object. This may allow the lookup to be resolved.

How do a use a method of this kind in F# ?

Upvotes: 2

Views: 248

Answers (1)

Foole
Foole

Reputation: 4860

From my comment:

let GetCustomer (sql : string) : Customer = ..

It is the "sql" it is having trouble identifying the type of, not the return value.

Upvotes: 4

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