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Chapter 1. The Type Traits Introspection Library

Edward Diener

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at

Table of Contents

Header Files
Why the TTI Library ?
General Functionality
Macro metafunction name generation considerations
Macro Metafunctions
Introspecting an inner type
Introspecting an inner class template
Using the has_template_(xxx) metafunction
Introspecting member data
Introspecting member function
Introspecting static member data
Introspecting static member function
Introspecting inner data
Introspecting an inner function
Nested Types
Nested Types and Function Signatures
Enclosing Type
An example using the Macro Metafunctions
Introspecting Function Templates
Header <boost/tti/gen/has_data_gen.hpp>
Header <boost/tti/gen/has_function_gen.hpp>
Header <boost/tti/gen/has_member_data_gen.hpp>
Header <boost/tti/gen/has_member_function_gen.hpp>
Header <boost/tti/gen/has_static_member_data_gen.hpp>
Header <boost/tti/gen/has_static_member_function_gen.hpp>
Header <boost/tti/gen/has_template_gen.hpp>
Header <boost/tti/gen/has_type_gen.hpp>
Header <boost/tti/gen/member_type_gen.hpp>
Header <boost/tti/gen/namespace_gen.hpp>
Header <boost/tti/has_data.hpp>
Header <boost/tti/has_function.hpp>
Header <boost/tti/has_member_data.hpp>
Header <boost/tti/has_member_function.hpp>
Header <boost/tti/has_static_member_data.hpp>
Header <boost/tti/has_static_member_function.hpp>
Header <boost/tti/has_template.hpp>
Header <boost/tti/has_type.hpp>
Header <boost/tti/member_type.hpp>
Testing TTI

Welcome to the Boost Type Traits Introspection library, abbreviated TTI.

TTI is a library which provides the ability to introspect by name the elements of a type at compile time.

TTI works through macros generating metafunctions. Metafunctions are class templates of a particular syntax, having a nested 'type' member. So wherever in C++ class templates can occur, TTI macros can be used. The metafunctions generated by TTI are no different from any other metafunction as defined by the Boost MPL library.

The metafunctions generated by TTI are used to introspect elements of a type at compile time, always passing at minimum to each metafunction the enclosing type being introspected.

The name of the library has been chosen because the library offers compile time functionality on a type, similar to the Boost Type Traits library, and because the functionality the library offers is the ability to introspect a type about the existence of a specific element within that type.

I use the word "introspect" in a very broad sense here. Normally computer language introspection means initially asking for information to be returned by name, which can then further be used to introspect for more specific information. In the TTI library one must always know and supply the name, and use the functionality provided for the correct type of inner element to find out if that particular named entity exists.

You may prefer the term "query" instead of "introspection" to denote what this library does, but I use terminology based on the word "introspect" throughout this documentation.

The functionality of the library may be summed up as:

  • Provide the means to introspect a type at compile time using a set of macros. Each macro takes the name of the type's element and generates a metafunction which can be subsequently invoked to determine whether or not the element exists within the type. These generated metafunctions will be called "macro metafunctions" in the documentation.
  • Provide the means to create a typedef for a type which may not exist. This typedef type can be used as a type in the metafunctions of the library without producing compile-time errors.

The library is dependent on Boost PP, Boost MPL, Boost Type Traits, and Boost Function Types.

The library is also dependent on the variadic macro support of the Boost PP library if the variadic macros in the library are used.

The library is a header only library.

Since the dependencies of the library are all header only libraries, there is no need to build a library in order to use the TTI library.

There are is a single header file, boost/tti/tti.hpp, which includes all the header files in the library.

There are also separate specific header files for each of the elements to be introspected by the library. This allows for finer-grained inclusion of the nested elements to be introspected. These header files are:

Table 1.1. TTI Header Files

Introspected Element

Specific Header File



Class Template


Member data


Member function


Static member data


Static member function






Member Type Creation



Last revised: April 17, 2017 at 02:29:08 GMT