lamda not finding string

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tshad

Given that a.Value is a string and dr is a DataRow

Just curious why this works:

var temp = Formats.Find(a => a.Value == (string)dr[0]);

And this doesn't

var temp = Formats.Find(a => a.Value == dr[0]);

The only difference is that I am not casting it.

If the 2nd one was a casting problem, I would expect an error - but I don't
get one. Temp is just = null.

Thanks,

Tom
 
Given that a.Value is a string and dr is a DataRow

Just curious why this works:

var temp = Formats.Find(a => a.Value == (string)dr[0]);

And this doesn't

var temp = Formats.Find(a => a.Value == dr[0]);

The only difference is that I am not casting it.

If the 2nd one was a casting problem, I would expect an error - but I don't
get one. Temp is just = null.

Thanks,

Tom
Click to expand...

I haven't look at the documentation, but my guess is
- dr[0] returning an object type, so you need a cast.
- assuming Formats is of type List<T>, then Formats.Find will return a
default(T) when the search failed. If 'a' is of reference type, will you
get a null.

Regards.
 
Given that a.Value is a string and dr is a DataRow

Just curious why this works:

var temp = Formats.Find(a => a.Value == (string)dr[0]);

And this doesn't

var temp = Formats.Find(a => a.Value == dr[0]);

The only difference is that I am not casting it.
Click to expand...

The first does string==string, which checks if the strings
contains the same char sequence.

The second does object==object, which checks if it is the same
object.

Arne
 
kndg said:
Given that a.Value is a string and dr is a DataRow

Just curious why this works:

var temp = Formats.Find(a => a.Value == (string)dr[0]);

And this doesn't

var temp = Formats.Find(a => a.Value == dr[0]);

The only difference is that I am not casting it.

If the 2nd one was a casting problem, I would expect an error - but I
don't
get one. Temp is just = null.

Thanks,

Tom
Click to expand...

I haven't look at the documentation, but my guess is
- dr[0] returning an object type, so you need a cast.
- assuming Formats is of type List<T>, then Formats.Find will return a
default(T) when the search failed. If 'a' is of reference type, will you
get a null.
Click to expand...

I understand the casting issue.

But normally, you get an error if you don't cast it. In this case, it went
through normally.

Thanks,

Tom
 
tshad said:
[...]
But normally, you get an error if you don't cast it. In this case, it went
through normally.
Click to expand...

You also don't get an error if you do this:

void MethodA(object obj) { }

void MethodB()
{
string str = "Foo";

MethodA(str);
}

Same thing is going on in your code example. There's no need to cast if
there's an applicable method for the type(s) given.

More generally, upcasting (to the less-derived types) does not actually
require an explicit cast. The implicit cast always exists. You only
need an explicit cast when downcasting, to more-derived types.

Pete
 
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