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c#visual-studioresharper

Is it possible to get a warning if return value is not used?

I have an extension method which returns a value. In this case, it should set a specific bit in a byte:

public static byte SetBit(this byte b, int bitNumber, bool value)
{
    if (value)
    {
        return (byte)(b | (1 << bitNumber));
    }
    return (byte)(b & ~(1 << bitNumber));
}

The returned value needs to be assigned to a variable again, because I cannot combine this and ref:

byte myByte = 3;
myByte = myByte.SetBit(1, false);

It is easy to forget the assignment by accident. Someone might think that the method changes the value directly.

For a String.Replace, ReSharper/Visual Studio(?) is warning me that the Return value of pure method is not used:

String

Is this also possible for my method in some way?

Solution

  • Update:

    Now there is a PureAttribute in the System.Diagnostics.Contracts namespace.

    [Pure]
public byte Foo()
{
    //...
}

    Pre .NET Standard 2.0 Answer:

    There seems to be a Nuget Package for ReSharper Annotations.

    This includes a MustUseReturnValueAttribute:

    [MustUseReturnValue("Use the return value to...")]
public byte Foo()
{    
}

    As @Kirk Woll pointed out in the comments, it is also possible to write a custom Roslyn Analyzer.