I have been given a sample statement:
MyClass myclass = 3;
How is it possible to make this a valid statement? What code do I need to include in MyClass to support the implicit conversion from an int?
views:
304answers:
5
+14
A:
You need an implicit conversion operator:
public class MyClass
{
private readonly int value;
public MyClass(int value)
{
this.value = value;
}
public static implicit operator MyClass(int value)
{
return new MyClass(value);
}
}
Personally I'm not a huge fan of implicit conversions most of the time. Occasionally they're useful, but think carefully before putting them in your code. They can be pretty confusing when you're reading code.
On the other hand, when used thoughtfully, they can be amazingly handy - I'm thinking particularly of the conversions from string to XName and XNamespace in LINQ to XML.
Jon Skeet
2010-08-11 11:42:57
that's actually pretty slick.
0A0D
2010-08-11 11:46:18
They're confusing for classes for suresies. When used consistently with immutable structs, though, it is in fact not confusing, but very powerful. `FeetAndInches length = "10\'-3/16\""` is pretty obvious and leaves no room for question as to how it functions.
Michael Meadows
2010-08-11 11:54:19
@Michael: Actually it does. What does it do if the input string is null? Or empty? Or contains garbage? In each case, does it throw or does it return a nonsensical value? These answers are non-obvious to anyone reading the code, so you probably should not use an implicit operator there. (Of course, an implicit operator going the opposite way would be different, but then there’s already `ToString()` for that.)
Timwi
2010-09-19 01:35:45
@Timwi I think there's room for consistency by convention. I like to make sure that all of my structs have an uninitialized state `var feetAndInches = FeetAndInches.Empty`. This is also the default value. You can't assign null to a struct, so that's not an issue. If you assign a null string variable or otherwise unparseable string, then throw a parse exception. If you do this consistently, there shouldn't be confusion, and your code becomes much more readable.
Michael Meadows
2010-09-20 12:01:08
A:
You need to overload the implicit constructor operator:
public static implicit operator MyClass (int rhs)
{
MyClass c = new MyClass (rhs);
return c;
}
Simon P Stevens
2010-08-11 11:43:34
+5
A:
Here's how:
public class MyClass
{
public static implicit operator MyClass(int i)
{
return new MyClass(i);
}
}
This uses C# feature called implicit conversion operator.
Anton Gogolev
2010-08-11 11:43:45