This is how PHP has always worked, nothing to do with PHP 7.

The "logic" behind it is that an integer to string comparison will cast the string to an integer, thus giving you the result you observe. I think this is generally agreed to be not very useful, but also unlikely to change due to BC concerns.

You want === there otherwise you are comparing an int to a string and type coercion is going to make both sides int. The integer value of your string is 0 so 0 == 0.

Perhaps it would have helped to mention the context here as I'm trying to validate $_POST data.

For example a user submitting a value of 100 in a form. When PHP receives this it'll be a string.

For strict form validation, I was trying to make sure that int fields were only even processing an int response.

is_int() can't be used as when being used on a string, you'll get false. Is numeric can help, but this would also return true for a float.

Seems the best way around it is a bit of a hack:

<?php
<?php
$val_1 = 'test_string'; // Value is 'test_string'
$val_2 = (string) (int) $val_1;  // Value is '0' - This MUST be cast back to a string after typecasting the value to an int

if ($val_1 == $val_2) {
   // This now works as expected as we're comparing two strings
} else {
   ...
}

...or I suppose I could always do:
<?php
if (is_numeric($val_1) && !is_float($val_1)) {
    ...
}

This is really what the filter functions are for.

if (filter_var($_GET['val_1'], FILTER_VALIDATE_INT)) { ... }

or better:

if (filter_input(INPUT_GET, 'val_1', FILTER_VALIDATE_INT)) { ... }

I hadn't come across filter_input() before but that's exactly what I was after. Thanks