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Comment by coldpie | Hacker News Reader

Using Strings in any performance-critical situation, like object identifiers, is a newbie mistake (but also extremely common). That one shouldn't have happened. The others just strike me as things one learns about and fixes as the project matures and someone bothers to do a perf analysis to find the low-hanging fruit.

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…this is not very good advice? Using strings is fine, until it becomes a problem. People are going to read your comment and decide to change all their strings to integers or something at the cost of maintainability.

Thanks! Is the reason Strings impact performance because we can use smaller objects to do such work while Strings are larger?

It's not necessarily about the size itself, but more about the fact that it has to go through a memory allocator and it has to be GC'd if that's applicable, while a simple integer doesn't. Copies are more involved too.

Using strings for identifiers is almost always a bad idea.

Not something I had considered. So for example a UI component that might load 3 different versions based on a string identifier, should instead use an enum which maps to integers? I say an enum because this would preserve readability of the code.

Do you mean an API entirely internal to your application? In that case, yes, you probably want to use integers (enums), not Strings, to choose what to display.

If you are interfacing with other APIs that use Strings, it may make sense to just pass those through. For example loading files from disk or pulling up UI classes from the OS library using some String identifier or something. It's hard to say without more context.

Yes I was referring to internal APIs. Thanks

This is not true on iOS for most strings.

Why is that?

My guess is they are talking about some optimizations iOS does to make strings more performant, like interned string constants and tagged pointers. The majority of string usage probably falls under those.

Working with dynamically allocated strings, like reading from files, rendering from data bytes, working with C strings or building formatted strings, might have worse performance characteristics.

I think that's something the language does. I struggle to understand how iOS would do it.

iOS interns heavily across programming languages, and tagging and other small-string representations are available for non-C languages.

TIL!

Basically yeah. At a super rough level of understanding, the CPU can compare two integers with one instruction, but has to loop through a whole string[1] one character at a time to compare two strings for equality.

[1] Yeah yeah, CPUs & standard libraries are smarter than that, I know, I know. You get the point.

Most String comparisons are <5 instructions

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