GetType, typeof and is, to handle null and conversion

Question

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Type Checking: typeof, GetType, or is?

What is the difference between the following:

bool isLong (object a){
    return (a.GetType()==typeof(INT64));
}

bool isLong (object a){
    return (typeof(a)==typeof(INT64));
}

bool isLong (object a){
    return (a is INT64);
}

In addition. there is an option that a will be null. Does those functions can handle such case?

( I need to convert "value" to long? for example: c.CustomerId = (long?)value; )

can I use: long? id=(a as long?)

@thecoop: I added a question about null. Please see the question. — Naor, Mar 19 '11 at 13:32
Well, have you tried it in a test project to see what the behaviour is? — thecoop, Mar 19 '11 at 13:37

score 1 · Accepted Answer · answered Mar 19 '11 at 13:31

1

The first uses the instance a and will throw an exception if a is null. It compares the type using the Type class.

The second way won't work because typeof only works with type names, not instances.

In the last way, you are saying a is of type INT64. It not throw an exception if a is null. This is the preferred method.

However in your case, the conversion you could do

c.CustomerId = value as long?;

answered Mar 19 '11 at 13:31

Daniel A. White

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can I use: long? id=(a as long?)? – Naor Mar 19 '11 at 13:34
`is` always return `false` for `null`. – Julien Lebosquain Mar 19 '11 at 13:35
Absolutely - it will stick `null` into `id` if it can't do the conversion. – Daniel A. White Mar 19 '11 at 13:35

GetType, typeof and is, to handle null and conversion

1 Answers1