41 lines
2.2 KiB
Plaintext
41 lines
2.2 KiB
Plaintext
Option Strict On
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Partial Module PartialApplicationDynamic
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' Create a matching delegate type to simplify delegate creation.
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Delegate Function fsDelegate(Of TSource, TResult)(f As Func(Of TSource, TResult), s As IEnumerable(Of TSource)) As IEnumerable(Of TResult)
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Function fs(Of TSource, TResult)(f As Func(Of TSource, TResult), s As IEnumerable(Of TSource)) As IEnumerable(Of TResult)
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' This is exactly what Enumerable.Select does.
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Return s.Select(f)
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End Function
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Function ArrayConcat(Of T)(arr1 As T(), arr2 As T()) As T()
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Dim result(arr1.Length + arr2.Length - 1) As T
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Array.Copy(arr1, result, arr1.Length)
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Array.Copy(arr2, 0, result, 1, arr2.Length)
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Return result
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End Function
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' C# can define ParamArray delegates and VB can consume them, but VB cannot define them on its own.
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' The argument list of calls to the resulting function thus must be wrapped in a coerced array literal.
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' VB also doesn't allow Delegate as a type constraint. :(
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' The function is generic solely to ease use for callers. In this case generics aren't providing any type-safety.
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Function PartialApplyDynamic(Of TDelegate, TResult)(f As TDelegate, ParamArray args As Object()) As Func(Of Object(), TResult)
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Dim del = CType(CObj(f), [Delegate])
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Return Function(rest) CType(del.DynamicInvoke(ArrayConcat(args, rest).Cast(Of Object).ToArray()), TResult)
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End Function
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Sub Main()
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Dim args1 As Object = New Object() {0, 1, 2, 3}
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Dim args2 As Object = New Object() {2, 4, 6, 8}
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Dim fsf1 = PartialApplyDynamic(Of fsDelegate(Of Object, Object), IEnumerable(Of Object))(AddressOf fs, New Func(Of Object, Object)(AddressOf f1))
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Dim fsf2 = PartialApplyDynamic(Of fsDelegate(Of Object, Object), IEnumerable(Of Object))(AddressOf fs, New Func(Of Object, Object)(AddressOf f2))
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' The braces are array literals.
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Console.WriteLine("fsf1, 0-3: " & String.Join(", ", fsf1({args1})))
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Console.WriteLine("fsf1, evens: " & String.Join(", ", fsf1({args2})))
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Console.WriteLine("fsf2, 0-3: " & String.Join(", ", fsf2({args1})))
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Console.WriteLine("fsf2, evens: " & String.Join(", ", fsf2({args2})))
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End Sub
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End Module
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