Helpers

When to Use

• Utility logic is reused in multiple bounded contexts.
• Logic is stateless and does not need DB, HTTP, or authorization concerns.
• The same formatting/conversion logic appears in resources, views, and domain services.

When Not to Use

• Logic is used once in one method (keep it inline for clarity).
• Logic contains business rules (use Action/Service).
• Logic requires external dependencies or stateful configuration (prefer an injected service).

Preconditions

• Project PHP version supports typed signatures used by helper methods (nullable/union types as needed).
• Target formatter/parser dependencies are installed (for example nesbot/carbon for date parsing).
• Shared behavior and expected null handling are agreed before extracting to helper.
• Existing call sites are identified so extraction actually removes duplication.

Step-by-Step Helper Creation Checklist

• Confirm the logic is duplicated in at least 2 places.
• Confirm logic is utility-only (no business decisions, DB queries, or HTTP calls).
• Decide API surface: method name, input types, null behavior, return type.
• Implement typed method in app/Helpers/*Helper.php.
• Add focused unit tests including edge cases (null, invalid format, boundary values).
• Replace duplicate inline logic at call sites.
• Re-run PHPStan/PHPUnit for touched scope.

Rules

• Helper classes live in app/Helpers/
• Naming: PascalCase with a Helper suffix → StringHelper, MoneyHelper, DateHelper
• Helpers are for utilities needed in multiple places across the project
• Static methods are preferred for pure stateless transformations
• Use instance helpers only when collaborators/config must be injected (locale, formatter strategy, tenant settings)
• As helper count grows, group by namespace (App\Helpers\Formatting\, App\Helpers\Conversion\)
• Never put business logic in helpers — use Actions or Services
• Never put database queries in helpers — use Model Scopes
• Never put HTTP requests in helpers — use Services

Static vs Instance Guidance

• Use static when output depends only on input arguments.
• Use instance methods when behavior depends on constructor-provided collaborators/config.
• Do not create instance helpers just to mimic service-container usage when no dependencies are needed.

Examples

namespace App\Helpers;

use Carbon\Carbon;

class DateHelper
{
    public static function format(mixed $date, string $format = 'd M Y'): ?string
    {
        if (is_null($date)) {
            return null;
        }

        return Carbon::parse($date)->format($format);
    }
}

namespace App\Helpers;

class MoneyHelper
{
    public static function format(int $amountInCents, string $currency = 'CHF'): string
    {
        return number_format($amountInCents / 100, 2) . ' ' . $currency;
    }
}

// Usage in a Resource
'created_at' => DateHelper::format($this->created_at),
'amount'     => MoneyHelper::format($this->amount_in_cents),

// Instance helper for injectable collaborators or config
namespace App\Helpers\Formatting;

class LocalizedMoneyFormatter
{
    public function __construct(
        private readonly string $defaultCurrency = 'CHF',
    ) {}

    public function format(int $amountInCents, ?string $currency = null): string
    {
        $resolvedCurrency = $currency ?? $this->defaultCurrency;

        return number_format($amountInCents / 100, 2) . ' ' . $resolvedCurrency;
    }
}

Testing Guidance

use App\Helpers\DateHelper;
use PHPUnit\Framework\Attributes\Test;
use Tests\TestCase;

class DateHelperTest extends TestCase
{
    #[Test]
    public function it_formats_dates_and_handles_null(): void
    {
        $this->assertSame('21 Jan 2026', DateHelper::format('2026-01-21', 'd M Y'));
        $this->assertNull(DateHelper::format(null));
    }
}

Anti-Patterns

• Putting business logic in a helper (belongs in an Action or Service)
• Putting database queries in a helper (use Model scopes instead)
• Using a helper for logic only needed in one place (keep it inline)
• Creating a catch-all AppHelper or Utils class — keep helpers domain-specific
• Silent null fallback that hides invalid upstream data

References

• Carbon Documentation
• Related: Actions/SKILL.md — for business logic
• Related: Resources/SKILL.md — helpers are commonly used for formatting in API resources

Null-Handling Pitfall (Before/After)

// BEFORE (anti-pattern): null silently becomes "now", masking missing data bugs
public static function format(?string $date, string $format = 'd M Y'): string
{
    return Carbon::parse($date)->format($format);
}

// AFTER: explicit null contract preserves correctness at call sites
public static function format(?string $date, string $format = 'd M Y'): ?string
{
    if ($date === null) {
        return null;
    }

    return Carbon::parse($date)->format($format);
}