oliverdavies.uk/source/_daily_emails/2023-08-20.md

---
title: >
    PHP types and assertions
pubDate: 2023-08-20
permalink: >-
    archive/2023/08/20/php-types-and-assertions
tags:
    - php
---

Following yesterday's email about input validation, guard clauses and assertion libraries, these can be used to compliment PHP's native types and checking.

For example:

```language-php
function createJourney(string $from, string $to, int $duration): void {
  var_dump($from, $to, $duration);
}
```

In this code, each parameter has a type, but there's no validation on the values.

If I run this:

```language-plain
createJourney('', '', -10);
```

I would get this output:

```language-plain
string(0) ""
string(0) ""
int(-10)
```

This is probably not what you want.

I expect `$to` and `$from` to be not empty and the duration to be greater than zero.

## Here's the thing

I can use an assertion library or throw my own Exceptions if the values pass the type checks but aren't what I need.

For example:

```language-php
function createJourney(string $from, string $to, int $duration): void {
  Assert::stringNotEmpty($from);
  Assert::stringNotEmpty($to);
  Assert::positiveInteger($duration);

  var_dump($from, $to, $duration);
}
```

Now, if an empty string or negative duration is passed - in my implementation or test code - an Exception will be thrown.