release resources by using a using statement

  • Thread starter Thread starter Tony Johansson
  • Start date Start date
T

Tony Johansson

Hello!

Below I have a simple using construction. When this go out of scope which
close will be called
is the one in TextReader or the one in StreamReader

It must be the one in TextReader otherwise it's very strange.
The reson I ask it that a book called step by step C# 2005 is saying that
close in StreamReader will be called which must be totally wrong.

using (TextReader reader = new StreamReader(fullPathname))
{
string line;
while ((line = reader.ReadLine()) != null)
{
source.Text += line + "\n";
}
}

//Tony
 
Tony said:
Below I have a simple using construction. When this go out of scope which
close will be called
is the one in TextReader or the one in StreamReader

It must be the one in TextReader otherwise it's very strange.
The reson I ask it that a book called step by step C# 2005 is saying that
close in StreamReader will be called which must be totally wrong.

using (TextReader reader = new StreamReader(fullPathname))
{
string line;
while ((line = reader.ReadLine()) != null)
{
source.Text += line + "\n";
}
}
Click to expand...

It calls StreamReader Close, because what you have is an instance
of StreamReader. This is how polymorphism works.

Arne
 
Tony Johansson said:
Below I have a simple using construction. When this go out of scope which
close will be called
is the one in TextReader or the one in StreamReader

It must be the one in TextReader otherwise it's very strange.
The reson I ask it that a book called step by step C# 2005 is saying that
close in StreamReader will be called which must be totally wrong.

using (TextReader reader = new StreamReader(fullPathname))
{
string line;
while ((line = reader.ReadLine()) != null)
{
source.Text += line + "\n";
}
}
Click to expand...

It will actually call TextReader.Dispose() which will in turn call the
virtual Dispose(bool) method - which is overridden by StreamReader.

I don't see why you thought it "must be totally wrong" however - the
whole point of polymorphism is that if StreamReader *did* override
TextReader.Dispose() (which it can't in this particular case, as
TextReader.Dispose is non-virtual) then the StreamReader implementation
would be called.
 
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