NotSchema.md

NotSchema

The NotSchema inverts another schema: parsing succeeds when the wrapped schema fails, and fails when it succeeds. It covers the JSON Schema not keyword.

Basic Usage

use Chubbyphp\Parsing\Parser;

$p = new Parser();

$schema = $p->not($p->string());

$data = $schema->parse(42);     // Returns: 42
$data = $schema->parse('test'); // Throws error (input matches the string schema)

How It Works

1. The input is parsed against the wrapped schema
2. If the wrapped schema fails, the original input is returned unchanged
3. If the wrapped schema succeeds, a not.match error is thrown

not is pure validation: the wrapped schema's coercions and transformations never leak into the output, and its output type is mixed — "anything except X" has no narrower type.

Common Patterns

Forbidden Value

$schema = $p->not($p->const('forbidden'));

$schema->parse('allowed');   // Returns: 'allowed'
$schema->parse('forbidden'); // Throws error

Excluding a Shape

$schema = $p->not($p->object([
    'deprecatedField' => $p->string(),
]));

Record Values That Are Not Strings

$schema = $p->record($p->not($p->string()));

$schema->parse(['key1' => 1, 'key2' => true]); // Returns: ['key1' => 1, 'key2' => true]
$schema->parse(['key1' => 'value1']);          // Throws error

Edge Cases

• null input: not($p->string()) accepts null, because null is not a string. To reject null as well, combine with another schema or use not($p->union([...])).
• nullable(): as on every schema, nullable() short-circuits null before validation — not($p->const(null))->nullable() returns null even though the wrapped schema matches it.
• Wrapped schemas that cannot fail: a wrapped schema with catch() or default() may always succeed, which makes the not schema always fail.
• Error details: when not fails, the wrapped schema succeeded, so there are no inner errors to report — the single not.match error is all there is.

Error Codes

Code	Description
not.match	Input matches the wrapped schema