Dispatcher.vb

<Extension> _
Public Class Dispatcher
    ' Methods
    Public Shared Function DispatchMethod(ByVal instance As Expression, ByVal methods As IEnumerable(Of MethodInfo), ByVal typeArguments As IList(Of Type), ByVal arguments As IList(Of Expression)) As MethodCallExpression
        Return (From t In (From m In methods Select New Candidate(instance, m, Nothing, arguments)).If(Of IEnumerable(Of Candidate))(_ => ((Not typeArguments Is Nothing) AndAlso typeArguments.Any(Of Type)()), DirectCast(s => (From _ In s
            Where (_.Method.IsGenericMethodDefinition AndAlso (_.Method.GetGenericArguments.Length = typeArguments.Count))
            Select _.Method.MakeGenericMethod(typeArguments.ToArray(Of Type)()).Let(Of MethodInfo, Candidate)(m => New Candidate(_.Instance, m, m.GetGenericParameterMap(), arguments))), Func(Of IEnumerable(Of Candidate), IEnumerable(Of Candidate)))).Where(Of Candidate)(Function (ByVal t As Candidate) 
            Dim CS$<>8__locals27 As <>c__DisplayClass26 = DirectCast(Me, <>c__DisplayClass26)
            Return IIf(Not IIf((Not instance Is Nothing), (Not t.Method.IsStatic OrElse t.Method.IsExtensionMethod()), t.Method.IsStatic), False, t.Method.GetParameters.If(Of ParameterInfo(), Boolean)(_ => t.Method.IsParamArrayMethod(), ps => (((t.Arguments.Count >= (ps.Length - 1)) AndAlso ps.SkipLast(Of ParameterInfo)(1).Zip(Of ParameterInfo, Expression, Boolean)(t.Arguments, (p, a) => Dispatcher.IsAppropriate(p.ParameterType, a.Type)).All(Of Boolean)(_ => _)) AndAlso EnumerableEx.Repeat(Of ParameterInfo)(ps.Last(Of ParameterInfo)()).Zip(Of ParameterInfo, Expression, Boolean)(t.Arguments.Skip(Of Expression)((ps.Length - 1)), (p, a) => Dispatcher.IsAppropriate(p.ParameterType.GetElementType, a.Type)).All(Of Boolean)(_ => _)), ps => ((CS$<>8__locals27.arguments.Count = ps.Length) AndAlso ps.Zip(Of ParameterInfo, Expression, Boolean)(CS$<>8__locals27.arguments, (p, a) => Dispatcher.IsAppropriate(p.ParameterType, a.Type)).All(Of Boolean)(_ => _))))
        End Function)
            Select t.If(Of Candidate)(_ => _.Method.IsGenericMethod, DirectCast(_ => Dispatcher.InferTypeArguments((From p In t.Method.GetParameters Select p.ParameterType), (From e In t.Arguments Select e.Type)).Let(Of Dictionary(Of Type, Type), Candidate)(m => New Candidate(_.Instance, _.Method.MakeGenericMethod(m.Values.ToArray(Of Type)()), m, _.Arguments)), Func(Of Candidate, Candidate))).If(Of Candidate)(_ => _.Method.IsParamArrayMethod(), DirectCast(_ => _.Method.GetParameters.Let(Of ParameterInfo(), Candidate)(Function (ByVal ps As ParameterInfo()) 
                Dim CS$<>8__locals3e As <>c__DisplayClass3d = DirectCast(Me, <>c__DisplayClass3d)
                Return ps.Last(Of ParameterInfo)().ParameterType.GetElementType.Let(Of Type, Candidate)(Function (ByVal et As Type) 
                    Dim classd1 As <>c__DisplayClass3d = CS$<>8__locals3e
                    Return New Candidate(CS$<>8__locals3e._.Instance, CS$<>8__locals3e._.Method, CS$<>8__locals3e._.TypeArgumentMap, DirectCast(CS$<>8__locals3e._.Arguments.Take(Of Expression)((ps.Length - 1)).Concat(Of Expression)(EnumerableEx.Return(Of NewArrayExpression)(Expression.NewArrayInit(et, DirectCast((From e In CS$<>8__locals3e._.Arguments.Skip(Of Expression)((ps.Length - 1)) Select IIf((e.Type Is et), DirectCast(DirectCast(e, Func(Of Expression, Expression)), IEnumerable(Of Expression)), DirectCast(DirectCast(Expression.Convert(e, et), Func(Of Expression, Expression)), IEnumerable(Of Expression)))), IEnumerable(Of Expression))))).ToArray(Of Expression)(), IList(Of Expression)))
                End Function)
            End Function), Func(Of Candidate, Candidate))).If(Of Candidate)(_ => (_.Method.IsExtensionMethod() AndAlso (Not _.Instance Is Nothing)), DirectCast(_ => New Candidate(Nothing, _.Method, _.TypeArgumentMap, _.Arguments.StartWith(Of Expression)(_.Instance).ToArray(Of Expression)()), Func(Of Candidate, Candidate))) Into t
            Order By t.Method.IsParamArrayMethod()
            Order By t.Method.IsExtensionMethod()
            Select t).ThenByDescending(Of Candidate, Integer)(t => t.TypeArgumentMap.Count).First(Of Candidate)().Let(Of Candidate, MethodCallExpression)(t => IIf((Not t.Instance Is Nothing), DirectCast(Expression.Call(t.Instance, t.Method, t.Arguments), Func(Of Candidate, MethodCallExpression)), DirectCast(Expression.Call(t.Method, t.Arguments), Func(Of Candidate, MethodCallExpression))))
    End Function

    <Extension> _
    Public Shared Function GetConvertibleTypes(ByVal type As Type) As IEnumerable(Of Type)
        Return EnumerableEx.Concat(Of Type)(New IEnumerable(Of Type)() { EnumerableEx.Generate(Of Type, Type)(type, t => (Not t Is Nothing), t => t.BaseType, _ => _), type.GetInterfaces, IIf(type.IsInterface, EnumerableEx.Return(Of Type)(GetType(Object)), Enumerable.Empty(Of Type)) })
    End Function

    <Extension> _
    Public Shared Function GetExtensionMethods(ByVal type As Type) As IEnumerable(Of MethodInfo)
        Return IIf(type.HasExtensionMethods(), type.GetMethods.Where(Of MethodInfo)(New Func(Of MethodInfo, Boolean)(AddressOf Dispatcher.IsExtensionMethod)), Enumerable.Empty(Of MethodInfo))
    End Function

    <Extension> _
    Public Shared Function GetGenericParameterMap(ByVal method As MethodInfo) As Dictionary(Of Type, Type)
        Return method.GetGenericMethodDefinition.GetGenericArguments.Zip(Of Type, Type, Tuple(Of Type, Type))(method.GetGenericArguments, New Func(Of Type, Type, Tuple(Of Type, Type))(AddressOf Tuple.Create(Of Type, Type))).ToDictionary(Of Tuple(Of Type, Type), Type, Type)(_ => _.Item1, _ => _.Item2)
    End Function

    <Extension> _
    Public Shared Function GetGenericParameterMap(ByVal type As Type) As Dictionary(Of Type, Type)
        Return type.GetGenericTypeDefinition.GetGenericArguments.Zip(Of Type, Type, Tuple(Of Type, Type))(type.GetGenericArguments, New Func(Of Type, Type, Tuple(Of Type, Type))(AddressOf Tuple.Create(Of Type, Type))).ToDictionary(Of Tuple(Of Type, Type), Type, Type)(_ => _.Item1, _ => _.Item2)
    End Function

    <Extension> _
    Public Shared Function HasExtensionMethods(ByVal type As Type) As Boolean
        Return Attribute.IsDefined(type, GetType(ExtensionAttribute))
    End Function

    Public Shared Function InferTypeArguments(ByVal parameters As IEnumerable(Of Type), ByVal arguments As IEnumerable(Of Type)) As Dictionary(Of Type, Type)
        Return (From _ In (From t In parameters
            Where (t.IsGenericParameter OrElse t.IsGenericType)
            Select t).Zip(Of Type, Type, IEnumerable(Of Tuple(Of Type, Type)))(arguments, (p, a) => IIf(p.IsGenericParameter, DirectCast(EnumerableEx.Return(Of Tuple(Of Type, Type))(Tuple.Create(Of Type, Type)(p, a)), Func(Of Type, Type, IEnumerable(Of Tuple(Of Type, Type)))), DirectCast(p.GetGenericArguments.Zip(Of Type, Type, Tuple(Of Type, Type))(a.GetConvertibleTypes().Single(Of Type)(t => (t.IsGenericType AndAlso (p.GetGenericTypeDefinition Is t.GetGenericTypeDefinition))).GetGenericArguments, New Func(Of Type, Type, Tuple(Of Type, Type))(AddressOf Tuple.Create(Of Type, Type))), Func(Of Type, Type, IEnumerable(Of Tuple(Of Type, Type)))))) Select _).Distinct(Of Tuple(Of Type, Type))().ToDictionary(Of Tuple(Of Type, Type), Type, Type)(_ => _.Item1, _ => _.Item2)
    End Function

    Public Shared Function IsAppropriate(ByVal parameter As Type, ByVal argument As Type) As Boolean
        Return IIf(parameter.IsGenericParameter, argument.GetConvertibleTypes().Let(Of IEnumerable(Of Type), Boolean)(ts => parameter.GetGenericParameterConstraints.All(Of Type)(c => ts.Contains(Of Type)(c))), argument.GetConvertibleTypes().If(Of IEnumerable(Of Type))(_ => parameter.ContainsGenericParameters, DirectCast(_ => (From t In _ Select IIf(t.IsGenericType, DirectCast(DirectCast(t.GetGenericTypeDefinition, Func(Of Type, Type)), Func(Of IEnumerable(Of Type), IEnumerable(Of Type))), DirectCast(DirectCast(t, Func(Of Type, Type)), Func(Of IEnumerable(Of Type), IEnumerable(Of Type))))), Func(Of IEnumerable(Of Type), IEnumerable(Of Type)))).Let(Of IEnumerable(Of Type), Boolean)(_ => (_.Contains(Of Type)(parameter) OrElse (parameter.IsGenericType AndAlso _.Contains(Of Type)(parameter.GetGenericTypeDefinition)))))
    End Function

    <Extension> _
    Public Shared Function IsExtensionMethod(ByVal method As MethodInfo) As Boolean
        Return Attribute.IsDefined(method, GetType(ExtensionAttribute))
    End Function

    <Extension> _
    Public Shared Function IsParamArrayMethod(ByVal method As MethodBase) As Boolean
        Return method.GetParameters.Let(Of ParameterInfo(), Boolean)(_ => (_.Any(Of ParameterInfo)() AndAlso Attribute.IsDefined(method.GetParameters.Last(Of ParameterInfo)(), GetType(ParamArrayAttribute))))
    End Function


    ' Nested Types
    Friend Class Candidate
        ' Methods
        Public Sub New(ByVal instance As Expression, ByVal member As MemberInfo, ByVal typeArgumentMap As IDictionary(Of Type, Type), ByVal arguments As IList(Of Expression))
            Me.Instance = instance
            Me.Member = member
            Me.TypeArgumentMap = IIf(typeArgumentMap <>  Nothing , typeArgumentMap, New Dictionary(Of Type, Type))
            Me.Arguments = arguments
        End Sub


        ' Properties
        Property Arguments As IList(Of Expression)
            Public Get
            Private Set(ByVal value As IList(Of Expression))
        End Property
        Public ReadOnly Property Field As FieldInfo
            Get
                Return TryCast(Me.Member,FieldInfo)
            End Get
        End Property

        Property Instance As Expression
            Public Get
            Private Set(ByVal value As Expression)
        End Property
        Property Member As MemberInfo
            Public Get
            Private Set(ByVal value As MemberInfo)
        End Property
        Public ReadOnly Property Method As MethodInfo
            Get
                Return TryCast(Me.Member,MethodInfo)
            End Get
        End Property

        Public ReadOnly Property [Property] As PropertyInfo
            Get
                Return TryCast(Me.Member,PropertyInfo)
            End Get
        End Property

        Public ReadOnly Property Type As Type
            Get
                Return TryCast(Me.Member,Type)
            End Get
        End Property

        Property TypeArgumentMap As IDictionary(Of Type, Type)
            Public Get
            Private Set(ByVal value As IDictionary(Of Type, Type))
        End Property
    End Class
End Class