Need help translating function from c# to vb.net

Question

I need some help translating this code from c# to vb.net:

    private static Action<int, int> TranslateOrigin(Action<int, int> f, int x, int y)
    {
        return (a, b) => f(a + x, b + y);
    }

The automatic translators I've found on the internet make a mess of it, producing:

Private Shared Function TranslateOrigin(f As Action(Of Integer, Integer), x As Integer, y As Integer) As Action(Of Integer, Integer)
    Return Function(a, b) f(a + x, b + y)
End Function

Which won't compile, complaining that "Expression doe not produce a value." I've been poking at it for a while now and haven't had any luck translating it, any help would be greatly appreciated.

+1 the automatic translators are rubbish at lambdas.

MarkJ
– MarkJ

2012-10-24 05:45:11 +00:00
Commented Oct 24, 2012 at 5:45 — MarkJ
– MarkJ, Commented Oct 24, 2012 at 5:45

Jay · Accepted Answer · 2012-10-23 23:01:39Z

4

I think this is a bit closer since it doesn't return a value, but rather an action. using a single line.

Public Shared Function TranslateOrigin(f As Action(Of Integer, Integer), x As Integer, y As Integer) As Action(Of Integer, Integer)
    Return Sub(a, b) f(a + x, b + y)
End Function

edited Oct 23, 2012 at 23:01

answered Oct 23, 2012 at 22:56

Jay

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Comments

Magnus · Accepted Answer · 2012-10-23 23:01:53Z

1

This should do it:

Private Shared Function TranslateOrigin(ByVal f As Action(Of Integer, Integer), ByVal x As Integer, ByVal y As Integer) As Action(Of Integer, Integer)
     Return Function (ByVal a As Integer, ByVal b As Integer) 
               f.Invoke((a + x), (b + y))
            End Function
End Function

edited Oct 23, 2012 at 23:01

answered Oct 23, 2012 at 22:51

Magnus

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Comments

Styxxy · Accepted Answer · 2012-10-23 22:59:53Z

You are aware that an Action(Of T1, T2) delegate does not return a value? If it is anyway what you want (though I don't see much of a point in it, with value types), you can use a Sub.

Encapsulates a method that has two parameters and does not return a value.

With a sub, that will give this code:

Private Shared Function TranslateOrigin(f As Action(Of Integer, Integer), x As Integer, y As Integer) As Action(Of Integer, Integer)
    Return Sub(a, b) f(a + x, b + y)
End Function

You probably want to return a value, therefor you'll need a Func(Of T1, T2, TResult) delegate. In your case, that would make:

Private Shared Function TranslateOrigin(f As Func(Of Integer, Integer, Integer), x As Integer, y As Integer) As Func(Of Integer, Integer, Integer)
    Return Function(a, b) f(a + x, b + y)
End Function

Calling it as below, will return the value 6 (as I guess is expected):

TranslateOrigin(Function(x, y) x + y, 1, 2)(1, 2)

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