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Micro-optimisation; ‘starts with single-character string’ vs str[0]
source link: https://stevedrivendevelopment.com/2015/10/22/micro-optimisation-starts-with-single-character-string-vs-str0/
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Micro-optimisation; ‘starts with single-character string’ vs str[0]
I’m writing code with very stringent performance characteristics, and it’s a string validation routine. One part is a short-cut that kicks in if we might potentially be looking at a JSON object or JSON array. I’d written
var mightBeJson = value.StartsWith("{") || value.StartsWith("[")) {
as a short-cut. Turned out that since this is almost the first thing that happened in the code, this made a massive, terrible hit on performance. Switching to treating the string as a char array makes a massive difference;
var mightBeJson = value[0] == '[' || value[0] == '{';
Night and day difference!
Takeaway — never compare single-character strings like “X” when you can compare chars like ‘X’ directly.
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