How to Compare Flags in C#?

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In .NET 4 there is a new method Enum.HasFlag. This allows you to write:

if ( testItem.HasFlag( FlagTest.Flag1 ) )
{
    // Do Stuff
}

which is much more readable, IMO.

The .NET source indicates that this performs the same logic as the accepted answer:

public Boolean HasFlag(Enum flag) {
    if (!this.GetType().IsEquivalentTo(flag.GetType())) {
        throw new ArgumentException(
            Environment.GetResourceString(
                "Argument_EnumTypeDoesNotMatch", 
                flag.GetType(), 
                this.GetType()));
    }

    ulong uFlag = ToUInt64(flag.GetValue()); 
    ulong uThis = ToUInt64(GetValue());
    // test predicate
    return ((uThis & uFlag) == uFlag); 
}

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