System.IOUtils.TPath.GetDocumentsPath + System.SysUtils.PathDelim + 'myfile';

PathDelim VS DirectorySeparatorChar

System.SysUtils.PathDelim was introduced in Delphi 6 / Kylix 1, as a means to enable the writing of platform independent code. The introduction of Kylix, the original Delphi Linux compiler, meant that for the first time Delphi code executed on a *nix platform, as well as its original target of Windows.
System.IOUtils.TPath.DirectorySeparatorChar is part of the IOUtils unit that was introduced more recently to support the current wave of cross-platform tooling, which supports MacOS, iOS, Android and will soon encompass Linux once more.
Where you have a choice between System.SysUtils and System.IOUtils, you are generally expected to use the latter. The System.IOUtils is the cross-platform unit for file system support. That said, you commonly would not use DirectorySeparatorChar directly, but instead would use methods like System.IOUtils.TPath.Combine.
--David Heffernan

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