Implement VB With statement in C#

Question

How would you create an extension method which enables me to do the following (warning: exteme pseudo-code)...

class FooBar
{
    Int32 Foo { get; set; }
    String Bar { get; set; }
}

new FooBar().With(fb => new Func<FooBar, Object>(instance =>
{
    // VB With magic
    // NOTE: The instance parameter HAS to be by reference
    instance.Foo = 10;
    instance.Bar;

    return new Object();
}));

If you could specify anonymous functions without a return type (void), the above would look much cleaner...

new FooBar().With(fb => new Func<FooBar, void>(instance =>
{
    instance.Foo = 10;
    instance.Bar;
}));

This is pseudo-code of the worst kind. But I hope you get the idea.

Fredrik Mörk · Accepted Answer · 2010-09-03 09:05:31Z

4

To specify anonymous methods without return type, use Action<T> instead of Func<T, TResult>:

new FooBar().With(new Action<FooBar>(instance =>
{
    instance.Foo = 10;
    instance.Bar;
}));

(I don't quite see the point in this particular case, but I take your word on the pseudo code part...)

Update
Full example for being complete:

The extension method:

public static void With<T>(this T input, Action<T> action)
{
    action(input);
}

Sample usage

new FooBar().With(fb =>
{
    fb.Foo = 10;
    fb.Bar = "some string";
});

Note that you don't need to explicitly declare the Action<FooBar>, the compiler figures that out. Should you wish to, for clarity, the call would look like this:

new FooBar().With<FooBar>(new Action<FooBar>(fb =>
{
    fb.Foo = 10;
    fb.Bar = "some string";
}));

edited Sep 3, 2010 at 9:05

answered Sep 3, 2010 at 8:50

Fredrik Mörk

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1 Comment

cllpse Over a year ago

How would the extension method look like?

TcKs · Accepted Answer · 2010-09-03 08:57:07Z

2

Maybe this will help:

new FooBar().With( fb=> {
    fb.Foo = 10;
    fb.Bar = fb.Foo.ToString();
} );

// ... somewhere else ...
public static void With<T>( this T target, Action<T> action ) {
    action( target );
}

answered Sep 3, 2010 at 8:57

TcKs

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4 Comments

Jamiec Over a year ago

oh snap! you got there first.

cllpse Over a year ago

So fb is by reference, and not by value, yes?

Jamiec Over a year ago

@roosteronacid - assuming T is a class then yes. If you want to enforce this put a constraint on the method where T : class. See answer below.

cllpse Over a year ago

Awesome! Exactly what I was looking for!

Jamiec · Accepted Answer · 2010-09-03 09:06:08Z

2

As you asked how to write the extension, here goes

public static void With<T>(this T target, Action<T> action) where T : class
{
   action(target);
}

Personally dont see what benefit this has, but fill yer boots!

edited Sep 3, 2010 at 9:06

answered Sep 3, 2010 at 9:00

Jamiec

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Comments

Paul Hadfield · Accepted Answer · 2010-09-03 08:49:07Z

1

How about just

return new FooBar{ Foo=10; };

answered Sep 3, 2010 at 8:49

Paul Hadfield

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2 Comments

cllpse Over a year ago

Updated my question. I need the instance by reference.

Paul Hadfield Over a year ago

To who ever did, it's a bit harsh to vote my answer down when it prompted an update in the question. It may not be relevant now with more information but at the time it was.

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