Frg.RoslynRanger 0.1.2-beta.1

Roslyn Ranger

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

Math.Round Analyzer

Description

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.

Pitfall

By default Math.Round uses rounding strategy MidpointRounding.ToEven, this is also called Banker's Rounding.

This can cause major issues within any system, especially systems that deal with monetary values.

Example

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);

Code Fix

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);