Swift Thinking [video]

Interesting that the Apple-provided sample app mentioned around 7 minutes in uses "~=" as a custom operator, given that it's already defined for use with pattern matching (match an input with some sort of pattern), and intended to be overloaded for that purpose. I wonder if this is just an oversight?

User-defined operators are bad when they betray our expectations of what they should be doing - and by that, I mean if they don't exist in textbooks which are decades/hundreds of years old (and thus, almost universally accepted as part of our languages/cultures), they're gimmicks. That includes =~ for matching regular patterns - nobody would ever expect this to be the case - only someone who has encountered it in an existing language will use it as such.

User defined functions have names that we can understand, because we already share a common language - English. If we started "making up our own words" for functions, then we're doing just as bad as user-defined operators - nobody will recognize what the hell we're doing without looking up their implementations. It's like reading obfusticated code, or code in some language you don't know. If every programmer invents his own operators, good luck ever getting shit done - people don't have the time to learn some arbitrary language you conjure up just for the sake of shaving a few characters off code. Nor should anyone need a PhD in mathematics to understand the strange notations in your examples/proofs.

Operators cannot be searched for in the same way ASCII text can - we need specialized search engines which don't ignore characters - and they generally need to be written on a per-language basis to be useful. I think the time wasted doing this far exceeds the benefits user-defined operators provide.

Also, many unicode characters look alike, and it may be possible to utilize this in malicious ways where arbitrary characters may be used - by assuming someone reading/reviewing code will not look up the code points of every character. Having a limited set of characters makes it pretty simple to distinguish each one, unless you have poor fonts and can't make out differences between 1,I,l etc.

Operators are useful for sure, but they're never necessary. More to the point, they are just functions - treating them specially is silly, because it's much more useful to abstract over functions of any arity than to abstract over only binary functions.