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Why does using += on a nullable type result in a FORWARD_NULL defect
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)
The Ask Question Wizard is Live!
Data science time! April 2019 and salary with experienceWhy does C# forbid generic attribute types?Why is Dictionary preferred over Hashtable in C#?Why is it important to override GetHashCode when Equals method is overridden?Which is preferred: Nullable<T>.HasValue or Nullable<T> != null?Nullable types and the ternary operator: why is `? 10 : null` forbidden?Type Checking: typeof, GetType, or is?Performance surprise with “as” and nullable typesThe += operator with nullable types in C#Why are generic and non-generic structs treated differently when building expression that lifts operator == to nullable?Why not inherit from List<T>?
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No doubt there are other, perhaps better ways to do this, but I'm trying to understand what is going on here.
In the below example, coverity is reporting a FORWARD_NULL defect on the fourth line.
double? foo = null;
double bar = 1.23;
foo += bar;
System.Windows.Point point = new System.Windows.Point(foo,bar);
it reports:
assign_zero: Assigning: foo = null.
on the foo += bar line.
in += Operator (C# Reference), I see that x += y is equivalent to x = x + y, and in Using nullable types (C+ Programming Guide), I see that
These operators [the binary operator] produce a null value if one or both operands are
null
so is that what is going on? foo += bar becomes foo = foo + bar and since foo is null, foo + bar is null?
c# nullable static-analysis coverity
asked Mar 8 at 15:09
Michael J.Michael J.
22418
add a comment |
No doubt there are other, perhaps better ways to do this, but I'm trying to understand what is going on here.
In the below example, coverity is reporting a FORWARD_NULL defect on the fourth line.
double? foo = null;
double bar = 1.23;
foo += bar;
System.Windows.Point point = new System.Windows.Point(foo,bar);
it reports:
assign_zero: Assigning: foo = null.
on the foo += bar line.
in += Operator (C# Reference), I see that x += y is equivalent to x = x + y, and in Using nullable types (C+ Programming Guide), I see that
These operators [the binary operator] produce a null value if one or both operands are
null
so is that what is going on? foo += bar becomes foo = foo + bar and since foo is null, foo + bar is null?
c# nullable static-analysis coverity
asked Mar 8 at 15:09
Michael J.Michael J.
22418
Yeah, foo remains as null
– Richard Boyce
Mar 8 at 15:13
3
Is the defect being reported on line three, or is line three evidence for a defect that comes later? Normally the forward null defect is reported at the location where a null dereference can throw, but there's no such dereference here.
– Eric Lippert
Mar 8 at 16:34
@Eric Lippert you are correct. The defect is reported a few lines later where foo is being dereferenced. I'll update the question
– Michael J.
Mar 8 at 20:02
OK good, but the program fragment you gave shouldn't even compile.Pointtakes a double, not a nullable double. There's no reason to run code through Coverity if it doesn't even compile!
– Eric Lippert
Mar 8 at 22:54
add a comment |
No doubt there are other, perhaps better ways to do this, but I'm trying to understand what is going on here.
In the below example, coverity is reporting a FORWARD_NULL defect on the fourth line.
double? foo = null;
double bar = 1.23;
foo += bar;
System.Windows.Point point = new System.Windows.Point(foo,bar);
it reports:
assign_zero: Assigning: foo = null.
on the foo += bar line.
in += Operator (C# Reference), I see that x += y is equivalent to x = x + y, and in Using nullable types (C+ Programming Guide), I see that
These operators [the binary operator] produce a null value if one or both operands are
null
so is that what is going on? foo += bar becomes foo = foo + bar and since foo is null, foo + bar is null?
c# nullable static-analysis coverity
asked Mar 8 at 15:09
Michael J.Michael J.
22418
No doubt there are other, perhaps better ways to do this, but I'm trying to understand what is going on here.
In the below example, coverity is reporting a FORWARD_NULL defect on the fourth line.
double? foo = null;
double bar = 1.23;
foo += bar;
System.Windows.Point point = new System.Windows.Point(foo,bar);
it reports:
assign_zero: Assigning: foo = null.
on the foo += bar line.
in += Operator (C# Reference), I see that x += y is equivalent to x = x + y, and in Using nullable types (C+ Programming Guide), I see that
These operators [the binary operator] produce a null value if one or both operands are
null
so is that what is going on? foo += bar becomes foo = foo + bar and since foo is null, foo + bar is null?
c# nullable static-analysis coverity
c# nullable static-analysis coverity
asked Mar 8 at 15:09
Michael J.Michael J.
22418
asked Mar 8 at 15:09
Michael J.Michael J.
22418
edited Mar 8 at 20:10
Michael J.
asked Mar 8 at 15:09
Michael J.Michael J.
22418
asked Mar 8 at 15:09
Michael J.Michael J.
22418
asked Mar 8 at 15:09
Michael J.Michael J.
22418
22418
Yeah, foo remains as null
– Richard Boyce
Mar 8 at 15:13
3
Is the defect being reported on line three, or is line three evidence for a defect that comes later? Normally the forward null defect is reported at the location where a null dereference can throw, but there's no such dereference here.
– Eric Lippert
Mar 8 at 16:34
@Eric Lippert you are correct. The defect is reported a few lines later where foo is being dereferenced. I'll update the question
– Michael J.
Mar 8 at 20:02
OK good, but the program fragment you gave shouldn't even compile.Pointtakes a double, not a nullable double. There's no reason to run code through Coverity if it doesn't even compile!
– Eric Lippert
Mar 8 at 22:54
add a comment |
Yeah, foo remains as null
– Richard Boyce
Mar 8 at 15:13
3
Is the defect being reported on line three, or is line three evidence for a defect that comes later? Normally the forward null defect is reported at the location where a null dereference can throw, but there's no such dereference here.
– Eric Lippert
Mar 8 at 16:34
@Eric Lippert you are correct. The defect is reported a few lines later where foo is being dereferenced. I'll update the question
– Michael J.
Mar 8 at 20:02
OK good, but the program fragment you gave shouldn't even compile.Pointtakes a double, not a nullable double. There's no reason to run code through Coverity if it doesn't even compile!
– Eric Lippert
Mar 8 at 22:54
Yeah, foo remains as null
– Richard Boyce
Mar 8 at 15:13
Yeah, foo remains as null
– Richard Boyce
Mar 8 at 15:13
3
3
Is the defect being reported on line three, or is line three evidence for a defect that comes later? Normally the forward null defect is reported at the location where a null dereference can throw, but there's no such dereference here.
– Eric Lippert
Mar 8 at 16:34
Is the defect being reported on line three, or is line three evidence for a defect that comes later? Normally the forward null defect is reported at the location where a null dereference can throw, but there's no such dereference here.
– Eric Lippert
Mar 8 at 16:34
@Eric Lippert you are correct. The defect is reported a few lines later where foo is being dereferenced. I'll update the question
– Michael J.
Mar 8 at 20:02
@Eric Lippert you are correct. The defect is reported a few lines later where foo is being dereferenced. I'll update the question
– Michael J.
Mar 8 at 20:02
OK good, but the program fragment you gave shouldn't even compile.
Point takes a double, not a nullable double. There's no reason to run code through Coverity if it doesn't even compile!– Eric Lippert
Mar 8 at 22:54
OK good, but the program fragment you gave shouldn't even compile.
Point takes a double, not a nullable double. There's no reason to run code through Coverity if it doesn't even compile!– Eric Lippert
Mar 8 at 22:54
add a comment |
1 Answer
1
active
oldest
votes
so is that what is going on? foo += bar becomes foo = foo + bar and
since foo is null, foo + bar is null?
Yes.
answered Mar 8 at 15:16
spodgerspodger
1,308913
add a comment |
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so is that what is going on? foo += bar becomes foo = foo + bar and
since foo is null, foo + bar is null?
Yes.
answered Mar 8 at 15:16
spodgerspodger
1,308913
add a comment |
so is that what is going on? foo += bar becomes foo = foo + bar and
since foo is null, foo + bar is null?
Yes.
answered Mar 8 at 15:16
spodgerspodger
1,308913
add a comment |
so is that what is going on? foo += bar becomes foo = foo + bar and
since foo is null, foo + bar is null?
Yes.
answered Mar 8 at 15:16
spodgerspodger
1,308913
so is that what is going on? foo += bar becomes foo = foo + bar and
since foo is null, foo + bar is null?
Yes.
answered Mar 8 at 15:16
spodgerspodger
1,308913
answered Mar 8 at 15:16
spodgerspodger
1,308913
answered Mar 8 at 15:16
spodgerspodger
1,308913
answered Mar 8 at 15:16
spodgerspodger
1,308913
1,308913
add a comment |
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Yeah, foo remains as null
– Richard Boyce
Mar 8 at 15:13
3
Is the defect being reported on line three, or is line three evidence for a defect that comes later? Normally the forward null defect is reported at the location where a null dereference can throw, but there's no such dereference here.
– Eric Lippert
Mar 8 at 16:34
@Eric Lippert you are correct. The defect is reported a few lines later where foo is being dereferenced. I'll update the question
– Michael J.
Mar 8 at 20:02
OK good, but the program fragment you gave shouldn't even compile.
Pointtakes a double, not a nullable double. There's no reason to run code through Coverity if it doesn't even compile!– Eric Lippert
Mar 8 at 22:54