Why do the StringBuilder Append methods return a StringBuilder object?

user_3726030 0
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So if you take a look at any of the Append methods of a 'StringBuilder', the return type is StringBuilder. Not a string or a count of lines or anything you might think could be even intuitively useful. Ostensibly (I haven't checked this yet), it's the same StringBuilder object that you just called the method on.

I can't really see a reason for that. Is there one?

stringbuilder c#
1 Answers

This is a simple form of what is called a "fluent interface" or "fluent API". (see This wikipedia article) APIs following that pattern allow chaining of methods, which may look weird in the beginning, but may make the code natural to read. Another well-known API implementing this is linq, where you can write things like

myList.Where(x => x.Element1 > 1).OrderBy(x => x.Element2).Select(x => x.Element3);

Or, as a really sophisticated sample of a fluent API, a task description from Nuke build:

Target CompileForMatlab => _ => _
    .Executes(() =>
    {
        MSBuild(s => s
                    .SetSolutionFile(Solution)
                    .SetConfiguration(Configuration)
                    .AddTargets("Restore,Build,Publish")
                    .SetProjectFile(Solution.GetProject("ExtendedLogParser"))
                    .SetOutDir(ArtifactsDirectory / "ExtendedLogParser")
                    .SetProperty("Platform", Platform)
                    .AddProperty("SelfContained", true)
                    .AddProperty("RuntimeIdentifier", "win10-x64")
                    .AddProperty("PublishDir", "../ExtendedLogParser")
                    .DisableNodeReuse());
    });
user_29057680
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