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Re: [DotGNU]fxcop

From: Rhys Weatherley
Subject: Re: [DotGNU]fxcop
Date: Sat, 1 May 2004 07:10:13 +1000
User-agent: KMail/1.4.3

On Saturday 01 May 2004 06:51 am, Marcus wrote:
> The "if (val.Length == 0)" does not seem very intuitive in the context of
> determine whether a string is empty or not. A better solution would seem to
> be to optimize the comparison of "if (val == String.Empty)".
> Also, my understanding was that all string constants declared in a program
> would be interned, so that a simple pointer comparison could be done.

Interning would apply to the "" or String.Empty part of the comparison, but 
not necessarily to the contents of "val".  A simple pointer comparison would 
fail on the following code:

       String x = " ";
       String y = x.Trim();
       if(Object.ReferenceEquals(y, "")) ...

i.e. calculated string results are not necessarily interned, and so their 
pointers may not be the same as interned strings.  It also varies from system 
to system a little bit (I had to use an empty StringBuilder to get the same 
effect under csc).

> Given all that, I'm not sure why the val.Length version is so much faster.

Portable.NET inlines "val.Length", converting it into a simple "fetch int from 
field" opcode.  Portable.NET also inlines string comparison, but it needs to 
do more work than a simple field fetch.



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