PHPStan Rules to Disallow Float proliferation in contexts where IEEE-754 rounding errors are not acceptable

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1.11.0 2024-01-14 16:22 UTC



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This library is a PHPStan plugin that disallows:

  • declaration of float properties
  • float method parameters
  • float method return types
  • assignment of float values to variables or properties

The reason for this restriction is that rounding errors coming from floating point arithmetic operations are not acceptable in certain business logic scenario, such as dealing with money, evaluating exam results, rocket science, etc.

An example of such problems can be seen with the following typical example:

var_dump((0.7 + 0.1) === 0.8); // output: bool(false)

This can mean no trouble at all, or a lot of trouble, depending on how many numbers you are running through your system, so it is advisable to avoid float for domains where rounding can potentially lead to trouble.

float is still perfectly acceptable in many programming contexts, and this ruleset should only be applied where it is critical not to introduce rounding errors.


composer require --dev roave/no-floaters


In your phpstan.neon configuration, add following section:

    - vendor/roave/no-floaters/rules.neon

Optionally, you can configure the library to disallow any float-producing expression at all, by adding following to your phpstan.neon:

    disallowFloatsEverywhere: true

If the above is enabled, given the following example-file.php contents:


$a = 1 / 3;

You should get something like following:

vendor/bin/phpstan analyse example-file.php -l 7
 1/1 [▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓▓] 100%

 ------ -----------------------------------------------------
  Line   example-file.php
 ------ -----------------------------------------------------
  3      Cannot assign float to $a - floats are not allowed.
 ------ -----------------------------------------------------

 [ERROR] Found 1 error

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