Explanation on closures

[sjoshi23@yahoo.com]

Hi All

Can someone clarify what is happening in these 2 code fragments ?

int i=0;

Action b = delegate {i++; Console.WriteLi ne("Within b() i= +
i.ToString());} ;

Action<inta = delegate(int j){ j++; Console.WriteLi ne("Within a(i) =
" + j.ToString());} ;

i++;
b();
// i now becomes 2

a(i);
// i is reported as 3 within a

Console.WriteLi ne("i = " + i.ToString());
// i still shows as 2 ****

So the question is why i changes for b and not for a ?

thanks
Sunit

[Jon Skeet [C# MVP]]

Re: Explanation on closures

<sjoshi23@yahoo .comwrote:

Can someone clarify what is happening in these 2 code fragments ?
>
int i=0;
>
Action b = delegate {i++; Console.WriteLi ne("Within b() i= +
i.ToString());} ;
>
Action<inta = delegate(int j){ j++; Console.WriteLi ne("Within a(i) =
" + j.ToString());} ;
>
i++;
b();
// i now becomes 2
>
a(i);
// i is reported as 3 within a
>
Console.WriteLi ne("i = " + i.ToString());
// i still shows as 2 ****
>
So the question is why i changes for b and not for a ?

The delegate created for b *captures* the i variable - in other words,
it can still make changes to it, and see changes in the rest of the
method.

The delegate created for a doesn't capture any local variables -
instead, a value is passed in as a parameter (just as it would be for
any normal method). Incrementing that parameter value doesn't change
the original variable's value.

--
Jon Skeet - <skeet@pobox.co m>
Web site: http://www.pobox.com/~skeet
Blog: http://www.msmvps.com/jon.skeet
C# in Depth: http://csharpindepth.com