In Advanced ABAP for RAP (ABAP RESTful Application Programming Model) development, inline data declaration refers to the ability to declare data structures directly within the definition of an ABAP class or interface, without the need to define them in separate data dictionary objects.

This feature allows developers to define data structures inline, right where they are needed, which can improve code readability and maintainability, especially for small or specialized data structures that are tightly coupled with the logic of a particular class or interface.

Here's an example of inline data declaration in ABAP for RAP:

CLASS lcl_example DEFINITION.

PUBLIC SECTION.

TYPES: BEGIN OF ty_inline_structure,

field1 TYPE string,

field2 TYPE i,

END OF ty_inline_structure.

DATA: inline_data TYPE ty_inline_structure.

ENDCLASS.

In this example, the ty_inline_structure type and inline_data variable are defined directly within the definition of the lcl_example class. This inline data declaration allows the data structure to be tightly coupled with the class, making it easier to understand and maintain the code.

Inline data declaration can be particularly useful in scenarios where the data structure is used only within a specific class or interface and doesn't need to be shared or reused across multiple objects.