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I had a recent code review that gave me some slightly surprising feedback. It was in an instantiable service class that had a number of fully encapsulated private methods. In other words, methods that didn't reference any higher level functions or variables. For a trivial example:

private decimal IncreaseByPercent(decimal original, int percentageIncrease)
{
    return original + ((original / 100) * percentageIncrease);
}

The feedback suggested that methods like this should be marked as static. It's not a suggestion I've come across before: indeed I've rarely used static methods outside of static classes. What would be the advantages of doing so?

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    Unfortunately this question was closed before I could finish writing my answer. In addition to the answers in the "duplicate", it looks like you are using C#. If so, there's a very good reason to mark a method as static if you can: performance. "After you mark the methods as static, the compiler will emit non-virtual call sites to these members ... [which] can achieve a measurable performance gain for performance-sensitive code.": msdn.microsoft.com/en-us/library/ms245046.aspx
    – David Arno
    Apr 17 '18 at 16:18
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    @DavidArno: The performance benefits are almost inconsequential in most cases. "Performance-sensitive code" is a special case. The real reason you mark private methods as static is to indicate that you won't be touching instance state. Apr 17 '18 at 16:52
  • @RobertHarvey, performance-sensitive code used to be a special case. The mass of crap added to C# 7.1 and 7.2 around passing structs by reference sadly shows those days are gone. Games and mobile (both of which are performance sensitive) is a big thing for MS these days and drives a lot of the C# language development.
    – David Arno
    Apr 17 '18 at 17:33
  • @DavidArno: I don't know anything about C# 7.x, but based on your description it seems that these new constructs are better to be avoided (at least in game development), not papered over with static calls. Apr 17 '18 at 17:38
  • In the future, specify your language, as "static" can have several meanings. Apr 18 '18 at 0:00

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