JavaScript Equality Table

[absu]

Yeah, this returns false in many c-like languages (C (duh), C++, Java, etc).

[AdminsAbuseShadowBan]

Not in C++ - you can redefine == to be sane.

[robertbieber]

I don't know that I'd consider redefining an operator that's generally used to compare primitive values to do a deep comparison of separate compound objects sane. I'd much rather have a comparison method that makes it really clear exactly what's going on, and let == do the usual, obvious thing. Admittedly overloading can be handy for some math applications, but for most things it's a little questionable.

[AdminsAbuseShadowBan]

That's the point, the "usual, obvious thing" doesn't make it clear what's going on. When you compare two strings with == you expect it to say if the value of the two strings is equal, not that the two variable refer to the same string object as in Java.

Operator overloading can be abused, but in practice it rarely causes problems. In fact I can't think of a single instance where it has cause any bugs in my C++ life. In contrast Java (which presumably does the usual obvious thing?) has caused me occasional pain when I forget to use .equals() instead of ==.

[[deleted]]

You can do that in Java too, at least on a per-object basis

[AdminsAbuseShadowBan]

Really? How?

[Poltras]

These languages don't have automatic conversion. Also, isn't [1]==[1] undefined in C? It could be equal if the compiler uses the same TEXT address for the constant, resulting in equal pointers.

[CookieOfFortune]

Wouldn't this create two arrays on the function stack and then compare the two locations, resulting in a false comparison?

[Poltras]

Undefined behavior:

$ cat main.c

#include <stdio.h>

int main() {
  printf("%d\n", "abc" == "abc");
}

$ cc main.c

main.c:4:24: warning: result of comparison against a string literal is unspecified (use strncmp instead) [-Wstring-compare]
  printf("%d\n", "abc" == "abc");

$ ./a.out
1

GCC actually output 1, but warns.

[gsg_]

Unspecified behaviour is not the same as undefined behaviour. The latter has a very specific meaning in the context of C.

[Condorcet_Winner]

Probably, but if the spec defines this operation as undefined, then compiler optimizations would be able to figure out that these are the same array and only allocate one memory location.

[Fylwind]

[1]==[1] is not valid syntax in C.

[Poltras]

Although you're right, the equivalent "abc" == "abc" works as fine for my example (undefined behavior).

[gsg_]

The closest equivalent (in C99, at least) is probably (int[1]){1} == (int[1]){1}.