Analysis of integer values (integral arithmetics)
ReSharper can track the flow of integer values through your code and report redundant or possibly erroneous statements. It supports all C# integral numeric types —
ulong — and warns you about the following issues:
relational/equality operators that always evaluate to
meaningless arithmetic operations, such as multiplication by
1or addition of
0(except literals or constants: ReSharper assumes that expressions like
x + 0are intentional),
possible division by
possible errors in invocations of
the above issues in enumeration types with the corresponding underlying types.
Toggle integer value analysis
Analysis of integer values is enabled by default. If necessary, you can disable it by clearing the Analyze integer arithmetic checkbox on the page of ReSharper options (Alt+R, O)
How it works
ReSharper narrows down the possible range of values for each integer according to possible outcomes of all statements and expressions that can produce or affect that integer. Let's consider some examples.
ReSharper can deduce that
temp < 0 in the example below will always evaluate to
false because Math.Abs always returns a non-negative value.
In the following example, ReSharper infers that by the last
return, the value of
input is in the range of
-100 ... 100, and when divided by a larger
divider, it will be truncated towards zero.
Refine analysis with annotations
There are two JetBrains.Annotations attributes (
[ValueRange(from, to)]) for analysis of integer values.
You can use these attributes with type members returning
int and with
int parameters to specify known constraints and thus improve analysis precision.
Here is an example of annotating the method parameter with [NonNegativeValueAttribute] to refine the analysis within the method body. Knowing that the parameter is non-negative, ReSharper can report all redundant operations on that parameter:
The following example demonstrates how annotating a method can help find redundant checks around its usages: