Let's say you have yourself a class like the following:
public sealed class StringToInt {
private string _myString;
private StringToInt(string value)
{
_myString = value;
} public static implicit operator int(StringToInt obj)
{
return Convert.ToInt32(obj._myString);
}
public static implicit operator string(StringToInt obj)
{
return obj._myString;
}
public static implicit operator StringToInt(string obj)
{
return new StringToInt(obj);
}
public static implicit operator StringToInt(int obj)
{
return new StringToInt(obj.ToString());
}
}
Will you then be able to write code like the following:
MyClass.SomeMethodThatOnlyTakesAnInt(aString);
without it stating that there is no implicit cast from string to int?
[Yes, i could test it myself but i thought i would put it out there and see what all of the gurus have to say]
I am fairly certain this is not possible under C# 3.0. The sections in the reference that covers conversions is 6.4. Namely, 6.4.4 "User-defined implicit conversions".
It only talks about conversions from S->T (and not S->T->U) which covers the cases such as:
StringToInt _t = "foo";
int t = _t;
and
int t = (StringToInt)"foo";
Where both of these cases only involve S->T (twice).
I am pretty sure this is not possible in C# 3.0. Allowing S->T->U would require much more work to be performed by the type matcher, at least following the algorithm specified.
No C# won't call more than one user defined implicit conversion. From the C# spec section 6.4.3:
Evaluation of a user-defined conversion never involves more than one user-defined or lifted conversion operator. In other words, a conversion from type S to type T will never first execute a user-defined conversion from S to X and then execute a user-defined conversion from X to T.
It does not appear to work. It requires at least one explicit cast. Oh well...
Typos in your snippet:
public StringToInt(string value)
{
_myString = value;
}
public static implicit operator int(StringToInt obj)
{
return Convert.ToInt32(obj._myString);
}
public static implicit operator string(StringToInt obj)
{
return obj._myString;
}
If aString
is of type StringToInt
, your usage should work.
来源:https://stackoverflow.com/questions/1611083/will-the-c-sharp-compiler-perform-multiple-implicit-conversions-to-get-from-one