PHP: Weak Typing - 2

In the Arithmetic module, we touched on the topic of weak typing.

PHP is a weakly typed language. It recognizes different data types (numbers, strings, etc.), but doesn't use them too strictly, it tries to convert data when it seems reasonable.

A particularly large number of automatic transformations take place when working with logical operations.

In PHP there are two simple rules by which conversions take place:

• 0, '0', '' (empty string), null are set to false. These values are called falsy.
• Everything else becomes true.

This works the other way as well: true and false are converted to other data types, depending on the situation:

<?php

print_r(true);

1

<?php

print_r(false);

(an empty string has been printed)

Another example:

<?php

print_r(0 || 1);

1

What happened here:

The OR operator only works with the bool type, but it's also given the numbers 1 and 0.

1. 0 is converted to false and 1 is converted to true.
2. The result false || true is true.
3. Now print_r() gets true, but it only works with strings (not bool).
4. true is converted to 1.
5. And the screen displays 1.

---

In one of our lessons, we looked at the comparison operators === and !== and mentioned that PHP also has the operators == and !=, but we shouldn't use them. The difference lies in type conversion:

<?php

var_dump('' === false); // => false
var_dump('' == false);  // => true

An empty string and false are different values, so the === operator says "false! they're not equal!

But the == operator converts types, making an empty string and false equivalent from its point of view. This conversion is implicit, so avoid the == and != operators whenever possible.

---

Remember the negation operator:

<?php

$answer = true;
var_dump(!$answer); // => false

When you use double negation !! the result value is equal to the initial value:

<?php

$answer = true;
var_dump(!!$answer); // => true

However, this is where type conversions also take place. Therefore, the result of a double negation will always be a bool. This trick is used to change the data type.

---

Different programming languages have different transformation rules. Some languages don't convert types themselves at all. Many features of PHP aren't really the best, but this is the historical legacy of the language. If it were created from scratch today, many of the rules and nuances would probably be quite different.

Instructions

Write an isFalsy() function that checks if the passed value is interpreted as false from PHP's point of view. To do this check, you need to compare false with the passed value using ==.

<?php

isFalsy(false);  // true
isFalsy(0);      // true
isFalsy('help'); // false
isFalsy(10);     // false

Tips

• Booleans