RoslynRanger is a collection of Roslyn analyzers designed to reduce pull request back and forth and help developers avoid common pitfalls in C# and .NET
The Math.Round analyzer warns you when you use Math.Round without specifying a MidpointRounding argument. The absence of this argument could lead to rounding behavior that might not be intended.
By default Math.Round uses rounding strategy MidpointRounding.ToEven, this is also called Banker's Rounding.
| Number | MidpointRounding.ToEven | MidpointRounding.AwayFromZero |
|---|---|---|
| 1.5 | 2.0 | 2.0 |
| 2.5 | 2.0 | 3.0 |
| -1.5 | -2.0 | -2.0 |
| -2.5 | -2.0 | -3.0 |
This can cause major issues within any system, especially systems that deal with monetary values.
When Math.Round is used without explicitly specifying the rounding strategy the analyzer will report a diagnostic.
var result1 = Math.Round(3.14159);
var result2 = Math.Round(3.14159, 2);The following examples will not report a diagnostic.
var result1 = Math.Round(3.14159, MidpointRounding.AwayFromZero);
var result2 = Math.Round(3.14159, MidpointRounding.ToEven);
var result3 = Math.Round(3.14159, MidpointRounding.ToZero);
var result4 = Math.Round(3.14159, 2, MidpointRounding.ToNegativeInfinity);
var result5 = Math.Round(3.14159, 2, MidpointRounding.ToPositiveInfinity);This analyzer provides an automatic code fix with defaults to MidpointRounding.AwayFromZero as the rounding strategy is a commonly expected.
From
var result1 = Math.Round(3.14159);
var result2 = Math.Round(3.14159, 2);To
var result1 = Math.Round(3.14159, MidpointRounding.AwayFromZero);
var result2 = Math.Round(3.14159, 2, MidpointRounding.AwayFromZero);