Data type(s) of the type parameter(s) in extension method '<methodname>' defined in '<typename>' cannot be inferred from these arguments because more than one type is possible

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Data type(s) of the type parameter(s) in extension method '<methodname>' defined in '<typename>' cannot be inferred from these arguments because more than one type is possible. Specifying the data type(s) explicitly might correct this error.

An attempt has been made to use type inference to determine the type (or types) of the type parameter (or parameters) in a call to a generic extension method. The compiler finds more than one possible data type for one or more of the type parameters, and it reports this error.

Note

When specifying arguments is not an option (for example, for query operators in query expressions), the error message appears without the second sentence.

The following code demonstrates the error.

Option Strict Off
Imports System.Runtime.CompilerServices
Module Module1
    Sub Main()

        Dim caller As New Class1
        '' Not valid.
        'caller.targetExtension(1, "2")

    End Sub

    <Extension()> _
    Sub targetExtension(Of T)(ByVal p0 As Class1, ByVal p1 As T, ByVal p2 As T)
    End Sub

    Class Class1
    End Class

End Module

Error ID: BC36655 (within LINQ queries) and BC36652 (outside queries)

To correct this error

  • If the error appears outside of a query, try specifying the data type of the type parameter or parameters explicitly:

    caller.targetExtension(Of Integer)(1, "2")
caller.targetExtension(Of String)(1, "2")

See Also

Concepts

Extension Methods (Visual Basic)

Generic Procedures in Visual Basic

Reference

Option Strict Statement