Consider switching from RuntimeInformation.IsOSPlatform(XYZ) to OperatingSystem.IsXYZ()

[adamsitnik]

In dotnet/runtime#40457 new methods that allow for instant OS checks were introduced:

namespace System
{
    public partial class OperatingSystem
    {
        // Primary
        public static bool IsOSPlatform(string platform);
        public static bool IsOSPlatformVersionAtLeast(string platform, int major, int minor = 0, int build = 0, int revision = 0);

        // Accelerators for platforms where versions don't make sense
        public static bool IsBrowser();
        public static bool IsLinux();

        // Accelerators with version checks

        public static bool IsFreeBSD();
        public static bool IsFreeBSDVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0);

        public static bool IsAndroid();
        public static bool IsAndroidVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0);

        public static bool IsIOS();
        public static bool IsIOSVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0);

        public static bool IsMacOS();
        public static bool IsMacOSVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0);

        public static bool IsTvOS();
        public static bool IsTvOSVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0);

        public static bool IsWatchOS();
        public static bool IsWatchOSVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0);

        public static bool IsWindows();
        public static bool IsWindowsVersionAtLeast(int major, int minor = 0, int build = 0, int revision = 0);
    }
}

All the IsXYZ methods (not IsXYZVersionAtLeast()) are basically returning constants and thanks to that, JIT is capable of performing dead code elimination:

if (OperatingSystem.IsWindows())
{
    // gets removed as dead code when running on non-windows OSes
}

For net5.0 libs/apps you might consider switching from the old API (RuntimeInformation.IsOSPlatform(XYZ)) to the new one.

/cc @davidfowl

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