PHP concatenation test

Dot: $a.$a
Curly braces: {$a}{$a}
Comma: $a,$a

Note: The test is based on 10 million concatenations for each case, so that after each subtest the output buffer is cleaned (PHP7). The result shows that concatenation with curly braces is ≈3% slower than dot concatenation. Concatenation with comma is the slowest, being ≈33% slower than dot concatenation. The results may vary.