PHP array vs [ ] in method and variable declaration

Question

I have a question about PHP syntax.

When defining functions and variables, which convention should I use?

I know they do the same thing in practice but I wou

Answer 1

just made a test to see how [] performs vs array() here is what I got

testing 1 million []s ( with $arr[] = [] )
started at : 1561298821.8754
ended at: 1561298822.6881
difference: 0.81266021728516 seconds 

testing 1 million array()s ( with array_push( $arr, array()) )
started at : 1561298822.6881
ended at: 1561298823.843
difference: 1.1549289226532 seconds 

testing 1 million []s ( again while the processor is hotter)
started at : 1561298823.8431
ended at: 1561298824.7448
difference: 0.9017219543457 seconds 

so [] performed about 20% faster