nexusphp/assert

Chainable type-safety assertions library.

v1.0.0 2026-03-14 17:11 UTC

Requires

• php: ^8.2

Requires (Dev)

• friendsofphp/php-cs-fixer: ^3.88
• kubawerlos/php-cs-fixer-custom-fixers: ^3.35
• nexusphp/cs-config: ^3.26
• nexusphp/tachycardia: ^2.4
• phpstan/extension-installer: ^1.4
• phpstan/phpstan: ^2.1
• phpstan/phpstan-phpunit: ^2.0
• phpstan/phpstan-strict-rules: ^2.0
• phpunit/phpunit: ^11.5 || ^12.5

MIT

• John Paul E. Balandan, CPA

README

Nexus Assert

This library provides efficient type assertions for input validation in a chainable, fluent, natural language way. This also provides static analysis support ensuring PHPStan can understand the asserted type.

Installation

composer require nexusphp/assert

Installing the PHPStan extension

You're all set if you are using phpstan/extension-installer.

Manual installation

If you don't want to use phpstan/extension-installer, include extension.neon in your project's PHPStan config:

includes:
    - vendor/nexusphp/assert/extension.neon

Usage

Use the static that() method of Nexus\Assert\Assert to start chaining expectations.

<?php

use Nexus\Assert\Assert;

function test(mixed $a, mixed $b, mixed $c): void
{
    Assert::that($a)->isString();
    // $a is now understood as string

    Assert::that($b)->isString()->isNumeric();
    // $b is now understood as numeric string

    Assert::that($c)->isInt()->not()->isNegativeInt();
    // $c is understood as int<0, max>
}

When an expectation fails, the method call will throw a Nexus\Assert\ExpectationFailedException object with the message formatted depending on the available context. By default, there are two available context:

Name	Description
value	The exported value of the argument passed to that()
type	The exported type of the argument passed to that()

List of Expectations

Methods	Available Context
contains(string $needle, ?string $message = null): self	value, needle
endsWith(string $needle, ?string $message = null): self	value, needle
hasMethod(string $method, ?string $message = null): self	value+, method=
hasOffset(int|string $key, ?string $message = null): self	value, key=
hasProperty(string $property, ?string $message = null): self	value+, property=
isArray(?string $message = null): self	value, type
isArrayKey(?string $message = null): self	value, type
isBool(?string $message = null): self	value, type
isCallable(?string $message = null): self	value, type
isCountable(?string $message = null): self	value, type
isFalse(?string $message = null): self	value, type
isFloat(?string $message = null): self	value, type
isIdentical(mixed $other, ?string $message = null): self	value, other, type
isInstanceOf(object|string $class, ?string $message = null): self	value, class, type
isInt(?string $message = null): self	value, type
isIterable(?string $message = null): self	value, type
isList(?string $message = null): self	value, type
isLowercaseString(?string $message = null): self	value, type
isMap(?string $message = null): self	value, type
isNaturalInt(?string $message = null): self	value, type
isNegativeInt(?string $message = null): self	value, type
isNonEmptyString(?string $message = null): self	value, type
isNull(?string $message = null): self	value, type
isNumeric(?string $message = null): self	value, type
isObject(?string $message = null): self	value, type
isPositiveInt(?string $message = null): self	value, type
isResource(?string $message = null): self	value, type
isScalar(?string $message = null): self	value, type
isString(?string $message = null): self	value, type
isTrue(?string $message = null): self	value, type
isUppercaseString(?string $message = null): self	value, type
matchesRegularExpression(string $pattern, ?string $message = null): self	value, pattern=
startsWith(string $needle, ?string $message = null): self	value, needle

Note

• The value context is always value-exported except when appended by + which means it is type-exported instead.
• The type context is always type-exported. In negated expectations, this context is omitted.
• Other context values are value-exported except when appended by = which means it is integrated as-is.

Available Expectation Classes

Nexus\Assert\Assert::that() returns an instance of Nexus\Assert\Expectation which is the base implementation of the Nexus\Assert\Expectable interface.

If you want to have a negated expectation, you can invoke not() on the expectation to return an instance of Nexus\Assert\NegatedExpectation.

<?php

use Nexus\Assert\Assert;

function test(mixed $a): void
{
    Assert::that($a)->isNumeric()->not()->isString();
    // $a is narrowed as either int or float
}

If you want to have a nullable expectation, that is, proceed with the expectation only if the input is not null, then you can invoke nullOr() on the base expectation.

<?php

use Nexus\Assert\Assert;

function test(mixed $a): void
{
    Assert::that($a)->nullOr()->isString();
    // $a is now understood as either string or null
}

Note

Currently, the not() and nullOr() methods can only be invoked on the base Expectation object. It is not yet available on the variant expectations. It can be considered in future versions.

Customising the Exporter

Nexus\Assert\Assert utilises the default implementation of Nexus\Assert\ExporterInterface - Exporter - to nicely export the value and type of the asserted input. If you need to do some customisations for your use case, you can implement your own exporter and let Assert use that.

<?php

use App\Exporter\MyExporter;
use Nexus\Assert\Assert;

Assert::setExporter(new MyExporter());

function foo(mixed $value): void
{
    Assert::that($value)->isBool();
}

Formatting the Exception Message

ExpectationFailedException accepts a templated message and the context when it is instantiated. You can modify the message by passing a template message as last argument to any expectation method. The context values are wrapped in curly braces with no in-between spaces.

<?php

use Nexus\Assert\Assert;

function test(mixed $a): void
{
    $message = 'Value "{value}" is not of type string'.
    Assert::that($a)->isString($message);
    // if this fails, the message would be something like:
    // Value "42" is not of type string.
}

When creating your custom messages, you are not compelled to use all available context. However, adding an unknown context for an expectation method will be useless as that won't be interpolated.

Resources

• Report issues
• Send pull requests

License

This library is licensed under MIT.