Information Technology Reference
In-Depth Information
public static implicit operator
MyType
(
String
aString)
{
return new
MyType
{ StringMember = aString };
}
}
See Item 28 for why conversion operators are bad; however, a user-defined
conversion operator is key to this issue. Consider this code (assume that
GetSomeStrings() returns a sequence of strings):
var
answer1 = GetSomeStrings().Cast<
MyType
>();
try
{
foreach
(
var
v
in
answer1)
Console
.WriteLine(v);
}
catch
(
InvalidCastException
)
{
Console
.WriteLine(
"Cast Failed!"
);
}
Before starting this item, you may have expected that GetSomeStrings()
.Cast<MyType>() would correctly convert each string to a MyType using
the implicit conversion operator defined in MyType. Now you know it
doesn't; it throws an InvalidCastException.
The above code is equivalent to this construct, using a query expression:
var
answer2 =
from
MyType
v
in
GetSomeStrings()
select
v;
try
{
foreach
(
var
v
in
answer2)
Console
.WriteLine(v);
}
catch
(
InvalidCastException
)
{
Console
.WriteLine(
"Cast failed again"
);
}
The type declaration on the range variable is converted to a call to
Cast<MyType> by the compiler. Again, it throws an InvalidCastException.
Here's one way to restructure the code so that it works:
