How to check if a dynamic object is null
I recently saw the following code, which puzzled me.
dynamic resultObj = SomeClass.run(arg);
if (resultObj == null || resultObj.ToString() == null)
{
/* Error handling */
}
Assuming SomeClass is your typical class (which does not override ToString()), is there a reason why the second part of the conditional would be necessary? Also, are there other potential issues with this code as it is?
c# dynamic null tostring
asked Dec 27 '16 at 23:23
SidSid
6116
add a comment |
I recently saw the following code, which puzzled me.
dynamic resultObj = SomeClass.run(arg);
if (resultObj == null || resultObj.ToString() == null)
{
/* Error handling */
}
Assuming SomeClass is your typical class (which does not override ToString()), is there a reason why the second part of the conditional would be necessary? Also, are there other potential issues with this code as it is?
c# dynamic null tostring
asked Dec 27 '16 at 23:23
SidSid
6116
What doesrunreturn? If it could possibly return a class that overridesToStringin a way that could return null then yes, the second check is necessary if you use the result ofToStringin yourifblock. Alldynamicmeans is "I don't know the type until runtime".
– D Stanley
Dec 27 '16 at 23:24
1
If it doesn't overrideToString, then it's callingobject.ToString()which returns the fully qualified name of the type of the Object - so yes - the.ToString() == nullcheck is not required.
– Rob♦
Dec 27 '16 at 23:31
Seems like poor design, to allow random classes to instantiate with random returns.
– Greg
Dec 27 '16 at 23:35
add a comment |
I recently saw the following code, which puzzled me.
dynamic resultObj = SomeClass.run(arg);
if (resultObj == null || resultObj.ToString() == null)
{
/* Error handling */
}
Assuming SomeClass is your typical class (which does not override ToString()), is there a reason why the second part of the conditional would be necessary? Also, are there other potential issues with this code as it is?
c# dynamic null tostring
asked Dec 27 '16 at 23:23
SidSid
6116
I recently saw the following code, which puzzled me.
dynamic resultObj = SomeClass.run(arg);
if (resultObj == null || resultObj.ToString() == null)
{
/* Error handling */
}
Assuming SomeClass is your typical class (which does not override ToString()), is there a reason why the second part of the conditional would be necessary? Also, are there other potential issues with this code as it is?
c# dynamic null tostring
c# dynamic null tostring
asked Dec 27 '16 at 23:23
SidSid
6116
asked Dec 27 '16 at 23:23
SidSid
6116
asked Dec 27 '16 at 23:23
SidSid
6116
asked Dec 27 '16 at 23:23
SidSid
6116
asked Dec 27 '16 at 23:23
SidSid
6116
6116
What doesrunreturn? If it could possibly return a class that overridesToStringin a way that could return null then yes, the second check is necessary if you use the result ofToStringin yourifblock. Alldynamicmeans is "I don't know the type until runtime".
– D Stanley
Dec 27 '16 at 23:24
1
If it doesn't overrideToString, then it's callingobject.ToString()which returns the fully qualified name of the type of the Object - so yes - the.ToString() == nullcheck is not required.
– Rob♦
Dec 27 '16 at 23:31
Seems like poor design, to allow random classes to instantiate with random returns.
– Greg
Dec 27 '16 at 23:35
add a comment |
What doesrunreturn? If it could possibly return a class that overridesToStringin a way that could return null then yes, the second check is necessary if you use the result ofToStringin yourifblock. Alldynamicmeans is "I don't know the type until runtime".
– D Stanley
Dec 27 '16 at 23:24
1
If it doesn't overrideToString, then it's callingobject.ToString()which returns the fully qualified name of the type of the Object - so yes - the.ToString() == nullcheck is not required.
– Rob♦
Dec 27 '16 at 23:31
Seems like poor design, to allow random classes to instantiate with random returns.
– Greg
Dec 27 '16 at 23:35
What does
run return? If it could possibly return a class that overrides ToString in a way that could return null then yes, the second check is necessary if you use the result of ToString in your if block. All dynamic means is "I don't know the type until runtime".– D Stanley
Dec 27 '16 at 23:24
What does
run return? If it could possibly return a class that overrides ToString in a way that could return null then yes, the second check is necessary if you use the result of ToString in your if block. All dynamic means is "I don't know the type until runtime".– D Stanley
Dec 27 '16 at 23:24
1
1
If it doesn't override
ToString, then it's calling object.ToString() which returns the fully qualified name of the type of the Object - so yes - the .ToString() == null check is not required.– Rob♦
Dec 27 '16 at 23:31
If it doesn't override
ToString, then it's calling object.ToString() which returns the fully qualified name of the type of the Object - so yes - the .ToString() == null check is not required.– Rob♦
Dec 27 '16 at 23:31
Seems like poor design, to allow random classes to instantiate with random returns.
– Greg
Dec 27 '16 at 23:35
Seems like poor design, to allow random classes to instantiate with random returns.
– Greg
Dec 27 '16 at 23:35
add a comment |
1 Answer
1
active
oldest
votes
A dynamic can be checked for null directly, but some circumstances can cause false answers. In order to check a dynamic for null, you should cast it as an object. For example,
dynamic post = SomeMethod();
if (post.modified == null){
//could return errors.
}
in order to check this property for null, you should do something like this: string.IsNullOrEmpty(Convert.ToString(post.Modified));
similarly, to check a dynamic for null, you should do something like this:
if ((object)post != null)
References:
https://ericlippert.com/2018/11/19/a-dynamic-definite-assignment-puzzle-part-2/
https://forums.asp.net/t/1592751.aspx?How+to+check+for+null+empty+strings+on+dynamic+objects+
So, by checking a resultObj.ToString() == null I believe this may convert the dynamic to an object and therefore enable for true null checking.
answered Nov 20 '18 at 19:20
Patrick KnottPatrick Knott
21325
custom operators may cause null checking on a dynamic object to return different logic than expected. stackoverflow.com/questions/7029699/…. You can get around this by casting to an object, I believe, feel free to downvote me and provide the reasons why I'm wrong.
– Patrick Knott
Nov 20 '18 at 21:34
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
A dynamic can be checked for null directly, but some circumstances can cause false answers. In order to check a dynamic for null, you should cast it as an object. For example,
dynamic post = SomeMethod();
if (post.modified == null){
//could return errors.
}
in order to check this property for null, you should do something like this: string.IsNullOrEmpty(Convert.ToString(post.Modified));
similarly, to check a dynamic for null, you should do something like this:
if ((object)post != null)
References:
https://ericlippert.com/2018/11/19/a-dynamic-definite-assignment-puzzle-part-2/
https://forums.asp.net/t/1592751.aspx?How+to+check+for+null+empty+strings+on+dynamic+objects+
So, by checking a resultObj.ToString() == null I believe this may convert the dynamic to an object and therefore enable for true null checking.
answered Nov 20 '18 at 19:20
Patrick KnottPatrick Knott
21325
custom operators may cause null checking on a dynamic object to return different logic than expected. stackoverflow.com/questions/7029699/…. You can get around this by casting to an object, I believe, feel free to downvote me and provide the reasons why I'm wrong.
– Patrick Knott
Nov 20 '18 at 21:34
add a comment |
A dynamic can be checked for null directly, but some circumstances can cause false answers. In order to check a dynamic for null, you should cast it as an object. For example,
dynamic post = SomeMethod();
if (post.modified == null){
//could return errors.
}
in order to check this property for null, you should do something like this: string.IsNullOrEmpty(Convert.ToString(post.Modified));
similarly, to check a dynamic for null, you should do something like this:
if ((object)post != null)
References:
https://ericlippert.com/2018/11/19/a-dynamic-definite-assignment-puzzle-part-2/
https://forums.asp.net/t/1592751.aspx?How+to+check+for+null+empty+strings+on+dynamic+objects+
So, by checking a resultObj.ToString() == null I believe this may convert the dynamic to an object and therefore enable for true null checking.
answered Nov 20 '18 at 19:20
Patrick KnottPatrick Knott
21325
custom operators may cause null checking on a dynamic object to return different logic than expected. stackoverflow.com/questions/7029699/…. You can get around this by casting to an object, I believe, feel free to downvote me and provide the reasons why I'm wrong.
– Patrick Knott
Nov 20 '18 at 21:34
add a comment |
A dynamic can be checked for null directly, but some circumstances can cause false answers. In order to check a dynamic for null, you should cast it as an object. For example,
dynamic post = SomeMethod();
if (post.modified == null){
//could return errors.
}
in order to check this property for null, you should do something like this: string.IsNullOrEmpty(Convert.ToString(post.Modified));
similarly, to check a dynamic for null, you should do something like this:
if ((object)post != null)
References:
https://ericlippert.com/2018/11/19/a-dynamic-definite-assignment-puzzle-part-2/
https://forums.asp.net/t/1592751.aspx?How+to+check+for+null+empty+strings+on+dynamic+objects+
So, by checking a resultObj.ToString() == null I believe this may convert the dynamic to an object and therefore enable for true null checking.
answered Nov 20 '18 at 19:20
Patrick KnottPatrick Knott
21325
A dynamic can be checked for null directly, but some circumstances can cause false answers. In order to check a dynamic for null, you should cast it as an object. For example,
dynamic post = SomeMethod();
if (post.modified == null){
//could return errors.
}
in order to check this property for null, you should do something like this: string.IsNullOrEmpty(Convert.ToString(post.Modified));
similarly, to check a dynamic for null, you should do something like this:
if ((object)post != null)
References:
https://ericlippert.com/2018/11/19/a-dynamic-definite-assignment-puzzle-part-2/
https://forums.asp.net/t/1592751.aspx?How+to+check+for+null+empty+strings+on+dynamic+objects+
So, by checking a resultObj.ToString() == null I believe this may convert the dynamic to an object and therefore enable for true null checking.
answered Nov 20 '18 at 19:20
Patrick KnottPatrick Knott
21325
edited Nov 20 '18 at 21:36
answered Nov 20 '18 at 19:20
Patrick KnottPatrick Knott
21325
answered Nov 20 '18 at 19:20
Patrick KnottPatrick Knott
21325
answered Nov 20 '18 at 19:20
Patrick KnottPatrick Knott
21325
21325
custom operators may cause null checking on a dynamic object to return different logic than expected. stackoverflow.com/questions/7029699/…. You can get around this by casting to an object, I believe, feel free to downvote me and provide the reasons why I'm wrong.
– Patrick Knott
Nov 20 '18 at 21:34
add a comment |
custom operators may cause null checking on a dynamic object to return different logic than expected. stackoverflow.com/questions/7029699/…. You can get around this by casting to an object, I believe, feel free to downvote me and provide the reasons why I'm wrong.
– Patrick Knott
Nov 20 '18 at 21:34
custom operators may cause null checking on a dynamic object to return different logic than expected. stackoverflow.com/questions/7029699/…. You can get around this by casting to an object, I believe, feel free to downvote me and provide the reasons why I'm wrong.
– Patrick Knott
Nov 20 '18 at 21:34
custom operators may cause null checking on a dynamic object to return different logic than expected. stackoverflow.com/questions/7029699/…. You can get around this by casting to an object, I believe, feel free to downvote me and provide the reasons why I'm wrong.
– Patrick Knott
Nov 20 '18 at 21:34
add a comment |
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What does
runreturn? If it could possibly return a class that overridesToStringin a way that could return null then yes, the second check is necessary if you use the result ofToStringin yourifblock. Alldynamicmeans is "I don't know the type until runtime".– D Stanley
Dec 27 '16 at 23:24
1
If it doesn't override
ToString, then it's callingobject.ToString()which returns the fully qualified name of the type of the Object - so yes - the.ToString() == nullcheck is not required.– Rob♦
Dec 27 '16 at 23:31
Seems like poor design, to allow random classes to instantiate with random returns.
– Greg
Dec 27 '16 at 23:35