Hyphenated keywords interacts badly with operator overloading
Reinier Zwitserloot
reinier at zwitserloot.com
Wed Jan 23 15:48:25 UTC 2019
I am a strong advocate of NOT including operator overloading in languages,
on the basis that so far, anytime a language adds it, even capable
programmers just cannot resist and make crazy APIs with it.
Nevertheless, Brian's hyphenated keywords proposal[1] interacts a bit badly
with operator overloading.
The specific trick with the hyphenated keyword (let's abbreviate that to
H-K) is that the tokenizer and parser kinda wanna interpret 'unsigned-int'
as 'subtract the expression 'int' from the expression 'unsigned', which is
always gobbledygook which is what makes the H-K proposal tick.
But if H-K is part of the language and operator overloading is added later,
you run into this uh-oh! situation (the implementation of how operator
overloading works is entirely strawman and not to be taken seriously; I
just needed some syntax to show off the problem is all):
given:
public class MyNumber implements OperatorOverloading {
/** This method would be invoked if you write (MyNumber)x - (MyNumber)y
*/
public MyNumber -(MyNumber other) { ... }
public void problem() {
MyNumber instance = ...;
System.out.println( this-instance );
}
}
Here the string 'this-instance' is intended as an H-K but it can be equally
well interpreted as an op-overload based invocation: The idea of 'call the
minus method, passing as params 'this' and 'instance', respectively).
I will shed absolutely no tears if we make the introduction of op
overloading in java more difficult by adopting H-K. But, perhaps it is wise
to at least make such a choice with open eyes: If H-K is adopted, this
might come up later.
[1]
http://mail.openjdk.java.net/pipermail/amber-spec-experts/2019-January/000945.html
--Reinier Zwitserloot
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