Another reason I don't like LINQ
-
Here's my error
System.ArgumentNullException: 'Value cannot be null.
Parameter name: values'... for this mess:
Columns.AddRange(obj.GetType().GetGenericArguments().FirstOrDefault()?.GetProperties().Where(p =>
{
return p.GetCustomAttributes(true).OfType().FirstOrDefault()?.Browsable ?? DefaultBrowsableState;
}).Select(p =>
{
return new ColumnHeader()
{
Name = p.Name,
Text = p.GetCustomAttributes(true).OfType().FirstOrDefault()?.DisplayName ?? p.Name
};
}).ToArray());The thing is, I know what it's trying to do, and the code makes sense to me even though I didn't write it. The LINQ isn't really that bad here. But the error message is just awful. I don't even know where to begin. Time to hand roll the same statement LINQless so I can debug it. So consider this my part 2 in why LINQ is for the birds.
Real programmers use butterflies
is that custom generated? because if you had to write that -"their's your sign"
Charlie Gilley <italic>Stuck in a dysfunctional matrix from which I must escape... "Where liberty dwells, there is my country." B. Franklin, 1783 “They who can give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety.” BF, 1759
-
I find that adding line breaks makes it a lot easier to read. Remember, you are writing for the next person to touch the code, not the computer. It is missing some Elvis operators, before the Where, the Select, and the ToArray, along with providing a value if the null propagates to the end. Also, you don't need the ToArray() as AddRange takes an IEnumerable<T>.
Columns
.AddRange(
obj.GetType()
.GetGenericArguments()
.FirstOrDefault()?.GetProperties()// need the Elvis operator ?.Where(p => { return p.GetCustomAttributes(true) .OfType() .FirstOrDefault()?.Browsable ?? DefaultBrowsableState; }) // need the Elvis operator ?.Select(p => { return new ColumnHeader() { Name = p.Name, Text = p.GetCustomAttributes(true) .OfType().FirstOrDefault()?.DisplayName ?? p.Name }; }) // don't need ToArray(), but need to provide a non-null value for AddRange() ?? Array.Empty());
"Time flies like an arrow. Fruit flies like a banana."
Matthew Dennis wrote:
It is missing some Elvis operators
It's not. If the
FirstOrDefaultreturnsnull, theGetPropertiesand subsequent calls won't execute. If it returns non-null,GetPropertieswill never returnnull:Type.GetProperties Method (System) | Microsoft Docs[^]:
Returns An array of PropertyInfo objects representing all public properties of the current Type. -or- An empty array of type
PropertyInfo, if the current Type does not have public properties.Similarly,
Wherewill never returnnull. If the input sequence isnull, it will throw an exception. If the input sequence is empty, or there are no matching elements, it will return an empty sequence. And the same applies toSelect- it will either throw an exception, or return a non-null sequence.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
-
A couple of possibly interesting bits of feedback, assuming that code comes from here: - Adding it to a WinForms app created with .NET Core 3.1 or .NET 5 and turning on nullable reference types finds 17 potential accidental nulls in the code from that SO post. But the Columns.AddRange call itself isn't one of them because WinForms wasn't built with NRT enabled. So the compiler decides it can't say one way or another if passing a null
valuesargument toAddRangeis okay. - Resharper catches the potential error whether you're using .NET Core/.NET 5 or .NET Framework. It even suggests a fix. The static analysis it's doing must look atAddRangeand notice that the first thing that method does is throw an exception ifvaluesis null.Ryan Peden wrote:
The static analysis it's doing must look at
AddRangeand notice that the first thing that method does is throw an exception ifvaluesis null.I suspect it's more likely that it has "external annotations" for the type in question. External Annotations—ReSharper[^] R# is already slow enough; if it had to do static analysis on every framework method you called, it would be completely unusable. :)
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
-
p.GetCustomAttributes(true).OfType()
I believe OfType<>() is returning a null.
honey the codewitch wrote:
The LINQ isn't really that bad here.
Actually, it's rather horrific. Not to mention what looks like completely unnecessary and probably wrong FirstOrDefault() usage, the reflection usage which looks like it could be simplified, and other confusing things. And the probably useless ToArray().
honey the codewitch wrote:
even though I didn't write it
Whew! ;)
Latest Articles:
Client-Side Type-Based Publisher/Subscriber, Exploring Synchronous, "Event-ed", and Worker Thread SubscriptionsMarc Clifton wrote:
I believe OfType<>() is returning a null.
Nope. :)
OfType<T>will throw an exception if the input sequence isnull. If the input sequence is empty, or doesn't contain any matching elements, it will return an empty sequence. It can never returnnull. Also, the elements within the returned sequence will never benull.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
-
I mean, yes. eventually. but it (as someone mentioned earlier but I forget who) reminds me of C++ template exceptions. The code and the exception couldn't seem more unrelated on the surface, and code that isn't communicative at face value is problematic, which is basically my point here. I have the same complaint about C++ templates and generic programming despite being in love with GP. I guess for me the power of GP outweighs the incomprehensibility of it but I just don't feel that way with LINQ.
Real programmers use butterflies
Try taking a look at the stack trace from an
asyncmethod (prior to .NET Core 2.1). :)
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
-
Matthew Dennis wrote:
It is missing some Elvis operators
It's not. If the
FirstOrDefaultreturnsnull, theGetPropertiesand subsequent calls won't execute. If it returns non-null,GetPropertieswill never returnnull:Type.GetProperties Method (System) | Microsoft Docs[^]:
Returns An array of PropertyInfo objects representing all public properties of the current Type. -or- An empty array of type
PropertyInfo, if the current Type does not have public properties.Similarly,
Wherewill never returnnull. If the input sequence isnull, it will throw an exception. If the input sequence is empty, or there are no matching elements, it will return an empty sequence. And the same applies toSelect- it will either throw an exception, or return a non-null sequence.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
actually that is incorrect. Only the chain of conditional operators is short circuited so if you have the expression
A()?.Bb()?.C().D()
and A() returns null the B and C will not be executed but there will be an attempt to execute D on a null object. Its sort of like async. You need to go all the way down. [Member access operators and expressions - C# reference | Microsoft Docs](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/member-access-operators#null-conditional-operators--and-)
"Time flies like an arrow. Fruit flies like a banana."
-
actually that is incorrect. Only the chain of conditional operators is short circuited so if you have the expression
A()?.Bb()?.C().D()
and A() returns null the B and C will not be executed but there will be an attempt to execute D on a null object. Its sort of like async. You need to go all the way down. [Member access operators and expressions - C# reference | Microsoft Docs](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/operators/member-access-operators#null-conditional-operators--and-)
"Time flies like an arrow. Fruit flies like a banana."
I'm not convinced. :)
static Foo A() => null;
public class Foo
{
public Foo B() => null;
public Foo C() => null;
public Foo D() => null;
}...
Foo result = A()?.B().C().D(); // result == null; no exception thrown.
Null conditional operator | C# Online Compiler | .NET Fiddle[^]
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
-
Try taking a look at the stack trace from an
asyncmethod (prior to .NET Core 2.1). :)
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
Yeah, those were always fun. Sometimes - when the code flow was complicated - I used to prototype using blocking calls just so I could debug the logic, and then slowly roll in the asynchronous methods (BeginWrite, etc) until it stopped working. :sigh:
Real programmers use butterflies
-
Marc Clifton wrote:
I believe OfType<>() is returning a null.
Nope. :)
OfType<T>will throw an exception if the input sequence isnull. If the input sequence is empty, or doesn't contain any matching elements, it will return an empty sequence. It can never returnnull. Also, the elements within the returned sequence will never benull.
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
This is illustrative of the point of my OP. If the error was clearer there would have been no confusion here.
Real programmers use butterflies
-
A couple of possibly interesting bits of feedback, assuming that code comes from here: - Adding it to a WinForms app created with .NET Core 3.1 or .NET 5 and turning on nullable reference types finds 17 potential accidental nulls in the code from that SO post. But the Columns.AddRange call itself isn't one of them because WinForms wasn't built with NRT enabled. So the compiler decides it can't say one way or another if passing a null
valuesargument toAddRangeis okay. - Resharper catches the potential error whether you're using .NET Core/.NET 5 or .NET Framework. It even suggests a fix. The static analysis it's doing must look atAddRangeand notice that the first thing that method does is throw an exception ifvaluesis null.That certainly makes using LINQ a bit nicer.
Real programmers use butterflies
-
I'm not convinced. :)
static Foo A() => null;
public class Foo
{
public Foo B() => null;
public Foo C() => null;
public Foo D() => null;
}...
Foo result = A()?.B().C().D(); // result == null; no exception thrown.
Null conditional operator | C# Online Compiler | .NET Fiddle[^]
"These people looked deep within my soul and assigned me a number based on the order in which I joined." - Homer
You may be correct. The documentation is a little vague on the extent of the short circuiting.
"Time flies like an arrow. Fruit flies like a banana."
-
You may be correct. The documentation is a little vague on the extent of the short circuiting.
"Time flies like an arrow. Fruit flies like a banana."
I checked this out and it appears that as long as the null occurs before a ?. or ?[] operator, the rest of the chain is short circuited and has a value of NULL. You learn something everyday. Thanks
"Time flies like an arrow. Fruit flies like a banana."
