Realistically speaking, there are no performance differences between single quotes and double quotes in PHP.
Any perceived differences will be so negligible that avoiding one or the other will be a complete waste of time.
Instead of obsessing over small micro-optimizations, developers should focus on writing good code that is clean and readable. They should also follow best practices.
It is extremely unlikely that using single quotes instead of double quotes is going to speed up your app.
If a bottleneck does occur, the cause will be something else. For example, a slow SQL query or a poorly configured web server.
Why it doesn’t matter.
- Modern benchmarks show no recognizable differences. In most cases, the results are old or remarkably inconclusive. That, or the differences are so tiny and insignificant that a human will never notice them.
- Even if it did matter (it doesn’t), in most production environments, you should be using a bytecode cache such as OPcache or APC.
- In the past, some of the developers behind PHP have publicly rejected the notion that there are any performance gains to be had by selectively choosing single quotes over double quotes.
- If there isn’t a variable in the double-quoted string, they will both generate the exact same opcode. In other words, PHP will treat them the same.
- There are much bigger “bottlenecks” to worry about. For example: Database queries, connections, API calls, large arrays and expensive loops are all far more likely to negatively impact the speed of your app.
Despite what certain “help” websites might say, this isn’t something that you need to worry about. Instead, you should focus on writing good code.