New .NET 4.0 Feature: Enum.HasFlag()

A minor inclusion to the new .NET 4.0 framework is the addition of the Enum.HasFlag() method. It behaves much like you'd expect, allowing you to check whether an enum instance contains a given flag.

public enum PacketOptions
    None       = 0x00, 
    All        = 0xff, 
    Compressed = 0x01, 
    Encrypted  = 0x02, 

PacketOptions opts = PacketOptions.All;
Assert.That(opts.HasFlag(PacketOptions.Compressed), Is.True);

Previously, flag testing was done using (opts & PacketOptions.Compressed) != 0, which was a little awkward because the != operator has higher precedence than &, hence the extraneous parenthesis.

If you'd attempted to implement your own HasFlag extension method, you'd have realized that it was not possible due to the way C# handles its type constraints (yep, I've been there).

Discovered via Reed Copsey.

Posted on November 10, 2009 from Calgary

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