Vix Validation

The validation module provides a modern, declarative, and type-safe way to validate data in C++.

It is designed for:

• backend APIs
• forms and user input
• configuration files
• domain models
• both beginners and advanced C++ developers

This module favors clarity, composability, and zero hidden magic.

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Philosophy

Validation in Vix is built around a few strong principles:

• Declarative: describe what is valid, not how to check it
• Type-safe: errors are caught at compile time when possible
• Composable: rules, schemas, and forms can be reused and combined
• Explicit: no exceptions, no implicit conversions
• Beginner-friendly but expert-ready

You can start with simple string validation and grow toward full form binding and cleaned output without changing your mental model.

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Core Concepts

The module is structured around five main building blocks:

Concept	Purpose
Validator<T>	Fluent validation of a single value
Schema<T>	Declarative validation rules for a struct
Form<T>	Bind raw input + validate + produce output
BaseModel<T>	CRTP helper for schema-driven models
ValidationResult / ValidationErrors	Structured error reporting

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1. Validating a Single Value

Use validate(field, value) for quick checks.

#include <vix/validation/Validate.hpp>

auto r = vix::validation::validate("email", email)
           .required()
           .email()
           .length_max(120)
           .result();

if (!r.ok())
{
  // handle r.errors
}

Examples:

• examples/simple_string.cpp
• examples/validate_string.cpp
• examples/validate_enum.cpp

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2. Schema: Declarative Validation for Structs

FieldSpec (beginner-friendly)

struct User
{
  std::string email;
  std::string password;

  static vix::validation::Schema<User> schema()
  {
    return vix::validation::schema<User>()
      .field("email", &User::email,
             vix::validation::field<std::string>()
               .required()
               .email()
               .length_max(120))
      .field("password", &User::password,
             vix::validation::field<std::string>()
               .required()
               .length_min(8)
               .length_max(64));
  }
};

Examples:

• examples/schema_fieldspec_basic.cpp
• examples/schema.cpp

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Lambda-based (expert-friendly)

.field("email", &User::email,
  [](std::string_view f, const std::string &v)
  {
    return vix::validation::validate(f, v)
      .required()
      .email();
  })

Examples:

• examples/schema_lambda_builder.cpp

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Cross-field validation

.check([](const User &u, ValidationErrors &errors)
{
  if (u.password != u.confirm)
  {
    errors.add("confirm",
               ValidationErrorCode::Custom,
               "passwords do not match");
  }
});

Examples:

• examples/schema_cross_field_check.cpp

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3. Parsed Validation (string to typed)

Examples:

• examples/parsed.cpp
• examples/form_parsed_age.cpp
• examples/validate_parsed_int.cpp

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4. Form: Bind + Validate + Output

Examples:

• examples/form_kv_basic.cpp
• examples/form_cleaned_output.cpp
• examples/form_bind2_generic_error.cpp

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5. BaseModel: Schema-driven Models (CRTP)

Examples:

• examples/basemodel_basic.cpp
• examples/basemodel_static_validate.cpp
• examples/basemodel_cross_field_check.cpp

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Error Model

Errors are structured, not strings.

ValidationError fields:

• field
• code
• message

Codes:

• Required
• Min, Max
• LengthMin, LengthMax
• Between
• Format
• InSet
• Custom

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Tests

Unit tests live in tests/.

Run:

ctest

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License

MIT Part of the Vix.cpp project.