Values and Types

At the heart of DDL is ddl::value, a container that can hold a value of several different types.

Unlike a regular C++ variable, whose type is fixed, a ddl::value can store different types of data during its lifetime.

Supported Types

DDL supports the following types:

Type	Description
nullptr_t	Represents a null value
bool	Boolean value (true or false)
int32_t	32-bit signed integer
int64_t	64-bit signed integer
float	Single-precision floating-point number
double	Double-precision floating-point number
char	Single character
std::string	Text
ddl::array	Collection of DDL values
ddl::object	Collection of key-value pairs

The ddl::value Type

A ddl::value stores exactly one of the supported types at a time.

For example:

ddl::value data = 42;

The value currently stores an integer. It can later hold something completely different:

data = "Hello, DDL!";

Now it stores a string instead.

This flexibility is provided by std::variant, which manages the currently stored type.

Type Checking

Use is<T>() to determine which type a value currently holds.

ddl::value data = 42;

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

The function returns:

• true if the stored type exactly matches T.
• false otherwise.

For example:

ddl::value data = 42;

std::cout << data.is<std::int32_t>() << '\n'; // 1
std::cout << data.is<double>() << '\n';       // 0

Important: is<T>() checks the stored type, not whether the value can be converted to T.

For example, an int32_t value can be converted to a double, but is<double>() still returns false.

Arrays and Objects

Two of DDL's supported types are containers:

• ddl::array is an alias for std::vector<ddl::value>.
• ddl::object is an alias for std::unordered_map<std::string, ddl::value>.

Because their elements are ddl::value instances, both containers can hold different types and support nested structures.

See Arrays and Objects for more details.