Quick Start

This guide introduces the basic features of DDL through a few examples.

Creating Values

DDL provides a unified ddl::value type that can store several different data types.

ddl::value a = 42;
ddl::value b = "Hello, DDL!";
ddl::value c = true;
ddl::value d = nullptr;

Checking Types

Use is<T>() to check which type a value currently stores.

ddl::value data = 42;

if (data.is<std::int32_t>()) {
    std::cout << "The value stores an int32_t.\n";
}

Converting Values

Use as<T>() to retrieve a value in a requested type.

ddl::value data = 42;

int number = data.as<int>();
std::string text = data.as<std::string>();

Conversions follow DDL's documented conversion rules. Unsupported conversions throw exceptions.

Working with Arrays

Unlike regular C++ arrays or vectors, a DDL array can contain values of different types.

ddl::array values = {
    42,
    "Hello",
    true,
    nullptr,
    ddl::array{10, 20, 30}
};

ddl::value data = values;

Each element is a ddl::value, so arrays can contain different types and even other arrays or objects.

You can retrieve an array using as<ddl::array>().

Working with Objects

Objects store key-value pairs using string keys.

ddl::object person = {
    {"name", "Alice"},
    {"age", 20},
    {"isStudent", true}
};

ddl::value data = person;

Values inside objects can themselves be arrays or other objects.

Printing Values

Use the stream insertion operator to print a value.

ddl::value data = ddl::object{
    {"name", "Alice"},
    {"age", 20},
    {"skills", ddl::array{"C++", "Python"}}
};

std::cout << data << '\n';

Output:

{
  "skills": [
    C++,
    Python
  ],
  "age": 20,
  "name": Alice
}

DDL recursively formats arrays and objects, making nested data easier to read.

Note: Object property order is unspecified because DDL uses std::unordered_map.

What's Next?

Explore Values and Types to understand the data model in more detail.