Re^4: Logical/defined or as lvalue

[jo37]

... implementing the "Elvis operator" ... as $x ? $x : $y

Actually, I read the opposite from the Wiki article:

... the Elvis operator expression A ?: B is approximately equivalent to the ternary conditional expression A ? A : B

... something like ... x = f() ?: g() ... is equivalent to ... the conditional ternary operator x = f() ? f() : g() except that it does not evaluate f() twice if it yields truthy.

Accentuations by me.

[ikegami]

That makes PHP's Elvis operator a value-preserving logical-OR operator, like Perl's ||.

According to the article, || also has this function in Common Lisp, Clojure, Lua, Object Pascal, Python, Ruby, and JavaScript. It's rather disingenuous to call the article "Elvis operator".

In C, || is normalizes the value to 0 or 1.

[jo37]

In retrospective, I shouldn't have brought up || as I don't see any use for an lvalue expression X || Y neither, which would be equivalent to the "Elvis operator".

A possible novelty could be a binary operator that:

• acts like defined(X) ? X : Y
• yields an lvalue, provided X and Y are lvalues
• evaluates X only once
If X // Y was an lvalue, it would satisfy these criteria. As it currently isn't, it could hardly break anything as such usage doesn't compile. No new operator, just an extension. In a Perlish sense: One more way to do it.

[ikegami]

Everything I said about || also applies to //. You only mention backwards-compatibility which wasn't even an issue I raised.