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Just when you think you've seen everything...
public SearchCriteria() : this(2000, 1) {}
...this is a default constructor for the SearchCriteria object... but what is that stuff after it... I can't find any documentation of this feature because searching for colon operator only gives me articles about inheritance of classes and interfaces. What are the implications of this construct, and what does it do...
There is another constructor that takes two integers. Is this the same as calling that one with 2000 and 1 as default values? If it is, I'm confused as to the purpose of this notation, when you could just as easily initialize those values "normally" or call the other constructor within this one, or something. There must be a reason for this colon thingy?
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Jasmine2501 wrote: Is this the same as calling that one with 2000 and 1 as default values?
Well, not default values but actual values, but, yes.
Jasmine2501 wrote: or call the other constructor within this one
No, you can't call another constructor in the code, that's the purpose of the special syntax.
Experience is the sum of all the mistakes you have done.
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It calls the constructor in the current class that has two int parameters and initializes them with the values 2000 and 1. You can fall through these constructors many times as in the following example:
public SearchCriteria() : this(2000, 1) {}
public SearchCriteria(int value, int otherValue) : this(value, otherValue, 20) {}
public SearchCriteria(int value, int otherValue, int finalValue)
{
_value = value;
_otherValue = otherValue;
_finalValue = finalValue;
}
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I should also point out that this is covered in books such as C# Step-by-Step (Microsoft Press). i.e. it is a very basic concept in the language that perhaps you might want to revise.
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I guess in my particular case, it didn't make a lot of sense because, for this particular class, it's the same as:
public SearchCriteria() {
m_year = 2000;
m_month = 1;
}
And in my mind this is much more readable and efficient. If the thing was doing more work with the values, I could understand the use of this construct.
The other constructor looks like:
public SearchCriteria(int yr, int mo) {
m_year = yr;
m_month = mo;
}
I think it's some contractor's idea to getting more hours, making the code harder to read, and hoping that the company will be dependent on him in the future. I'm seeing quite a few things which are obviously that kind of trick, but this one got me interested as to whether there was a good reason for it or not. This particular class is way overblown... it's one of those classes that could have just as easily been a struct, because it doesn't actually do any processing, it's only an object to aggregate some values together and it never actually does anything with those values besides store them.
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There is a rationale for using this construct:
Imagine the SearchCriteria class is modified to include additional initializations:
private string m_whereClause;
public SearchCriteria(int yr, int mo)
{
m_year = yr;
m_month = mo;
m_searchRX = new Regex(....); // precompile search criteria
m_resultCache = null;
}
using SearchCriteria() : this(2000, 1) {} keeps the change and additional code in one place.
Maybe this does not make any sense for the class you are using, but generally I would recommend using the this(...) in such a scenario.
We are a big screwed up dysfunctional psychotic happy family - some more screwed up, others more happy, but everybody's psychotic joint venture definition of CP
blog: TDD - the Aha! | Linkify!| FoldWithUs! | sighist
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Yes I agree. It does seem handy in that case, and I'll keep it in mind if that kind of situation ever arises. In this particular case though, it's just weird.
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I have the following code:
public enum LogLevel { Quiet=0, Noise=1, Verbose=2 };
private LogLevel IntToLogLevel(int value, LogLevel defaultValue)
{
LogLevel enumValue = defaultValue;
if (Enum.IsDefined(typeof(LogLevel), value))
{
enumValue = (LogLevel)value;
}
return enumValue;
}
I want to make the IntToLoglevel() function generic enough to use for any enum type. Is what I want to do possible?
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001
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<font color="Blue">static</font> <font color="Blue">void</font> Main<font color="DarkBlue">(</font><font color="Blue">string</font><font color="DarkBlue">[]</font> args<font color="DarkBlue">)</font>
<font color="DarkBlue">{</font>
LogLevel ll <font color="DarkBlue">=</font> IntToLogLevel<font color="DarkBlue"><</font>LogLevel<font color="DarkBlue">></font><font color="DarkBlue">(</font><font color="Red">2</font><font color="DarkBlue">,</font> LogLevel<font color="DarkBlue">.</font>Noise<font color="DarkBlue">)</font><font color="DarkBlue">;</font>
Console<font color="DarkBlue">.</font>WriteLine<font color="DarkBlue">(</font>ll<font color="DarkBlue">)</font><font color="DarkBlue">;</font>
LogLevel ll2 <font color="DarkBlue">=</font> IntToLogLevel<font color="DarkBlue"><</font>LogLevel<font color="DarkBlue">></font><font color="DarkBlue">(</font><font color="Red">4</font><font color="DarkBlue">,</font> LogLevel<font color="DarkBlue">.</font>Noise<font color="DarkBlue">)</font><font color="DarkBlue">;</font>
Console<font color="DarkBlue">.</font>WriteLine<font color="DarkBlue">(</font>ll2<font color="DarkBlue">)</font><font color="DarkBlue">;</font>
<font color="DarkBlue">}</font>
<font color="Blue">public</font> <font color="Blue">enum</font> <font color="Teal">LogLevel</font> <font color="DarkBlue">{</font> Quiet <font color="DarkBlue">=</font> <font color="Red">0</font><font color="DarkBlue">,</font> Noise <font color="DarkBlue">=</font> <font color="Red">1</font><font color="DarkBlue">,</font> Verbose <font color="DarkBlue">=</font> <font color="Red">2</font> <font color="DarkBlue">}</font><font color="DarkBlue">;</font>
<font color="Blue">static</font> T IntToLogLevel<font color="DarkBlue"><</font>T<font color="DarkBlue">></font><font color="DarkBlue">(</font><font color="Blue">int</font> value<font color="DarkBlue">,</font> T defaultValue<font color="DarkBlue">)</font>
<font color="DarkBlue">{</font>
T enumValue <font color="DarkBlue">=</font> defaultValue<font color="DarkBlue">;</font>
<font color="Blue">if</font> <font color="DarkBlue">(</font>Enum<font color="DarkBlue">.</font>IsDefined<font color="DarkBlue">(</font><font color="Blue">typeof</font><font color="DarkBlue">(</font>T<font color="DarkBlue">)</font><font color="DarkBlue">,</font> value<font color="DarkBlue">)</font><font color="DarkBlue">)</font>
<font color="DarkBlue">{</font>
enumValue <font color="DarkBlue">=</font> <font color="DarkBlue">(</font>T<font color="DarkBlue">)</font><font color="DarkBlue">(</font><font color="Blue">object</font><font color="DarkBlue">)</font>value<font color="DarkBlue">;</font>
<font color="DarkBlue">}</font>
<font color="Blue">return</font> enumValue<font color="DarkBlue">;</font>
<font color="DarkBlue">}</font>
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Brilliant. 
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001
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If you're using .NET 3.5, there's always this way:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace TestEnumExtension
{
public enum LogLevel { Quiet = 0, Noise = 1, Verbose = 2 }
class Program
{
static void Main(string[] args)
{
int outp = 12;
LogLevel level = outp.ConvertEnum(LogLevel.Quiet);
Console.WriteLine(level.ToString());
}
}
public static class Utility
{
public static T ConvertEnum<T>(this int value, T defaultValue)
{
T e = defaultValue;
if (Enum.IsDefined(typeof(T), value))
{
e = (T)(object)value;
}
return e;
}
}
}With thanks to Leppie for providing the basis for this with the answer above.
modified on Friday, February 01, 2008 5:39:53 PM
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Thats just plain evil, for too many reasons
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I've just edited the post so that you get the credit for the inspiration. It's only right and proper.
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John wrote most of the code 
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And I meant evil in a coding way, just imagine having to import the class everywhere, and have this pesky extension method on you int's! 
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It's all right - I didn't think anything else about the evil. I'm still of two minds as to extension methods.
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I dont think it's very usefull, except for the 2 LINQ cases. Now that I think of it, extension methods should be limited to interfaces only, that would make sense, else you just plain lazy to code decent
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leppie wrote: having to import the class everywhere
Yeah, I'm not very thrilled with extension methods either.
The compiler writer(s) should have spent the time working on virtual constructors. 
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I don't understand how that works. How is ConvertEnum a method of the int outp? Is it because of Linq?
"Why don't you tie a kerosene-soaked rag around your ankles so the ants won't climb up and eat your candy ass..." - Dale Earnhardt, 1997
-----
"...the staggering layers of obscenity in your statement make it a work of art on so many levels." - Jason Jystad, 10/26/2001
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It's because I've extended the type int to include a method called ConvertEnum. Have a look at extension methods to get an understanding as to how it works.
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Nice - take a look above for the extension method version.
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Those are pretty good, but I still prefer an Attribute, at least to reflect the original developer's intent.
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Hello,
Can someone point me towards a good tutorial which will walk me through how to
use C++ and Fortran code with/from C#.
Is it possible for me to use the object-files produced when compiling C++/Fortran
and use them in C#?
I'm looking to put a nice GUI around some old code.
Thanks........
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You can use C/C++ built DLLs in C#. Look into p/invoke. Assuming the fortran code was compiled into c++ compatible DLLs as well you could you it as well.
Otherwise [Microsoft is] toast in the long term no matter how much money they've got. They would be already if the Linux community didn't have it's head so firmly up it's own command line buffer that it looks like taking 15 years to find the desktop.
-- Matthew Faithfull
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