Using PHPStan to Find Type Errors

PHPStan can detect an invalid argument, nullable property access or wrong return type before those paths run in production.

What It Does

Compare a bad call with a type-correct replacement. Make an empty-array branch explicit in return calculations.

Requirements and Compatibility

Use a supported PHP runtime and install any third-party tool or extension explicitly shown in the examples. Commands should be run from the project root unless stated otherwise.

Syntax, Inputs and Results

The examples separate configuration, the smallest working operation and a realistic follow-up task. Adapt file paths and dependency versions to your own project.

Example 1: Basic Use

Compare a bad call with a type-correct replacement.

<?php
function takeId(int $id): int { return $id; }
// PHPStan reports the incorrect argument type here:
// takeId("ABC");
echo takeId(42);

Example 2: Another Case

Make an empty-array branch explicit in return calculations.

<?php
/** @param list<int> $scores */
function averageScore(array $scores): float {
    if ($scores === []) return 0.0;
    return array_sum($scores) / count($scores);
}
echo averageScore([4, 5, 6]);

Practical Example

Read a precise type-error report with source locations.

vendor/bin/phpstan analyse src --level=max --error-format=table
vendor/bin/phpstan analyse --debug

For production, apply the compatibility and edge-case limits described below.

Important Behavior and Edge Cases

Examine the exact reported line and check inferred types before adding a suppression rule.

Comparison with Related Functions and Tools

Common Beginner Mistakes

Key Takeaways

• PHPStan can detect an invalid argument, nullable property access or wrong return type before those paths run in production.
• Examine the exact reported line and check inferred types before adding a suppression rule.
• Keep application configuration, source code and validation tests under version control.

Use these examples as a starting point, then validate the result with the actual PHP build, dependencies and inputs used by your application.