|Perl: the Markov chain saw|
Depending on the font (and you can not always choose the one you like, especially online), you really have to look hard. I pretty much guarantee that code audits as well as helping out on SoPW will get a lot harder.
As for the typing effort, a character more or less really doesn't matter. Those of us who use non-english keyboards (so, most of us really) already have a hard time coding Perl and other programming languages. Some examples from my german keyboard:
In effect, a lot of the "standard" metacharacters require awkward right-hand-only acrobatics. I thought about using an english/american keyboard, but since i also require german umlauts that would just shift the problem. Just changing the keyboard layout in software is also a bit awkward, since then the printing on the keys does not match what i type (which i find rather confusing).
In short, i don't care if i have to type two or three characters, since something like ?-> is easier to read and harder to overlook (and in this case actually easier to type on my german keyboard as well).
And, from my personal view, i always associate ~ operations with some kind of regular expression stuff, whereas ? does not.
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