Programming Forums > Application Development > C#

lectricpharaoh · Jan 18th, 2007, 12:34 AM

Perhaps this will clear up some of the confusion. From the horse's mouth, there is no semantic difference between, say, int and System.Int32. I usually stick to the C# alias types (int, string, etc), but when I call the type's static methods, such as TryParse(), I usually use the .NET Framework type. This is just a style preference of mine.

What has been said about boxing and reference vs value types is worth remembering. Boxing should only happen if you explicitly do it (ie, with a cast), or implicitly assign a value type to an object type (including passing a value type as a parameter declared as an object type). If you're aware of when this occurs, it shouldn't be a problem, but if it's unclear, it can catch you out. In particular, comparisons will behave quite differently; for value types, it will be a true comparison, but for reference types, it will be a comparison of the references, not the actual values. Compare the following:

(Toggle Plain Text)

bool boxedCompare(object x, object y)
{
  return (x == y);
}

bool unboxedCompare(int x, int y)
{
  return (x == y);
}

The second will work fine when you pass it ints. The first will return true if and only if you're comparing something to itself, and that something was already a reference type. Comparing a value type to itself will cause the values to be boxed, creating two new (and different) references, thus returning false. This is exactly the kind of behavior that can cause problems if you're not clear on what's happening.

pegasus001 · Jan 18th, 2007, 5:03 AM

I dont really know how C# does this, but in java when you compared objects you only compared their address and if they pointed to the same address than they would return true, else false. I have always taken this thing a priori in C# too. Is it correct or not???????

Arevos · Jan 18th, 2007, 5:24 AM

In C#, this:

(Toggle Plain Text)

x == y

Is loosely equivalent to this in Java:

(Toggle Plain Text)

(x == null && y == null) || (x != null && x.equals(y))

Going in the opposite direction, this in Java:

(Toggle Plain Text)

x == y

Is equivalent to this in C#:

(Toggle Plain Text)

object.ReferenceEquals(x, y)

pegasus001 · Jan 18th, 2007, 5:34 AM

OOOOOps:o . Sorry for being so dumb. I will remember that. Thanx.

jonyzz · Jan 18th, 2007, 6:38 AM

Thank you for the info and links guys

it was useful to post my question here.

Jan 18th, 2007, 12:34 AM	#11
lectricpharaoh Caffeinated Neural Net Join Date: Jun 2005 Location: Dry west coast of Canada Posts: 1,031 Rep Power: 5	Perhaps this will clear up some of the confusion. From the horse's mouth, there is no semantic difference between, say, int and System.Int32. I usually stick to the C# alias types (int, string, etc), but when I call the type's static methods, such as TryParse(), I usually use the .NET Framework type. This is just a style preference of mine. What has been said about boxing and reference vs value types is worth remembering. Boxing should only happen if you explicitly do it (ie, with a cast), or implicitly assign a value type to an object type (including passing a value type as a parameter declared as an object type). If you're aware of when this occurs, it shouldn't be a problem, but if it's unclear, it can catch you out. In particular, comparisons will behave quite differently; for value types, it will be a true comparison, but for reference types, it will be a comparison of the references, not the actual values. Compare the following: (Toggle Plain Text) bool boxedCompare(object x, object y) { return (x == y); } bool unboxedCompare(int x, int y) { return (x == y); } bool boxedCompare(object x, object y) { return (x == y); } bool unboxedCompare(int x, int y) { return (x == y); } The second will work fine when you pass it ints. The first will return true if and only if you're comparing something to itself, and that something was already a reference type. Comparing a value type to itself will cause the values to be boxed, creating two new (and different) references, thus returning false. This is exactly the kind of behavior that can cause problems if you're not clear on what's happening. __________________ And once again, Probability proves itself willing to sneak into a back alley and service Drama as would a copper-piece harlot. - Vaarsuvius, Order of the Stick

Jan 18th, 2007, 5:03 AM	#12
pegasus001 Hobbyist Programmer Join Date: Nov 2006 Location: 163H Posts: 213 Rep Power: 2	I dont really know how C# does this, but in java when you compared objects you only compared their address and if they pointed to the same address than they would return true, else false. I have always taken this thing a priori in C# too. Is it correct or not??????? __________________ You never test the depth of a river with both feet. The believer is happy. The doubter is wise. Free speech carries with it some freedom to listen. The next generation will always surpass the previous one. It`s one of the never ending cycles of life.

Jan 18th, 2007, 5:24 AM	#13
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 5	In C#, this: (Toggle Plain Text) x == y x == y Is loosely equivalent to this in Java: (Toggle Plain Text) (x == null && y == null) \|\| (x != null && x.equals(y)) (x == null && y == null) \|\| (x != null && x.equals(y)) Going in the opposite direction, this in Java: (Toggle Plain Text) x == y x == y Is equivalent to this in C#: (Toggle Plain Text) object.ReferenceEquals(x, y) object.ReferenceEquals(x, y)

Jan 18th, 2007, 5:34 AM	#14
pegasus001 Hobbyist Programmer Join Date: Nov 2006 Location: 163H Posts: 213 Rep Power: 2	OOOOOps:o . Sorry for being so dumb. I will remember that. Thanx. __________________ You never test the depth of a river with both feet. The believer is happy. The doubter is wise. Free speech carries with it some freedom to listen. The next generation will always surpass the previous one. It`s one of the never ending cycles of life.

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Jan 18th, 2007, 6:38 AM	#15
jonyzz Programmer Join Date: Aug 2005 Location: null Posts: 40 Rep Power: 0	Thank you for the info and links guys it was useful to post my question here.

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Programming Forums > Application Development > C#

Difference between double and Double in C#