What is the difference between <> and !=

Question

In PHP to check non-equality (without checking type) you can do this:

if( A != B ) {
    DO SOMETHING;
}

But you can also do this, which has the same result:

if( A <> B ) {
    DO SOMETHING;
}

Is there any difference?

Does using != over <> change the evaluation in any way, shape, or form?

Answer 1

Forgetting documentation for a minute, let's check out the source code. Let's start with the scanner (lexer):

<ST_IN_SCRIPTING>"!="|"<>" {
    return T_IS_NOT_EQUAL;
}

So they parse to the same token. Let's check out the parser:

expr T_IS_NOT_EQUAL expr { zend_do_binary_op(ZEND_IS_NOT_EQUAL, &$$, &$1, &$3 TSRMLS_CC); }

So we know that the opcode that's fired is ZEND_IS_NOT_EQUAL...

Now, let's check out the operation:

static int ZEND_FASTCALL  ZEND_IS_NOT_EQUAL_SPEC_CONST_CONST_HANDLER(ZEND_OPCODE_HANDLER_ARGS)
{
    USE_OPLINE

    zval *result = &EX_T(opline->result.var).tmp_var;

    SAVE_OPLINE();
    ZVAL_BOOL(result, fast_not_equal_function(result,
        opline->op1.zv,
        opline->op2.zv TSRMLS_CC));

    CHECK_EXCEPTION();
    ZEND_VM_NEXT_OPCODE();
}

So there's literally no difference. Since they parse to the same token, they have exactly the same precedence. Since they use the same executor, and there's no decision point in the opcode routine, they execute identical code.

So yes, <> and != are 100% interchangeable, and there's absolutely no technical reason to use one over the other.

With that said, there is something significant to gain by being consistent. So I'd recommend just sticking with != and being done with it...