TBD: Explain why it is not usable

This library has never worked [on Borland 5.5.1 and 5.6.4], and the only tests that 'pass' are compile-fail tests failing for the wrong reasons!

Historically, Spirit supported a lot of compilers, including (to some extent) poorly conforming compilers such as VC6. Spirit v1.6.x will be the last release that will support older poorly conforming compilers. Starting from Spirit v1.8.0, ill conforming compilers will not be supported. If you are still using one of these older compilers, you can still use Spirit v1.6.x.

The reason why Spirit v1.6.x worked on old non-conforming compilers is that the authors laboriously took the trouble of searching for workarounds to make these compilers happy. The process takes a lot of time and energy, especially when one encounters the dreaded ICE or "Internal Compiler Error". Sometimes searching for a single workaround takes days or even weeks. Sometimes, there are no known workarounds. This stifles progress a lot. And, as the library gets more progressive and takes on more advanced C++ techniques, the difficulty is escalated to even new heights.

Spirit v1.6.x will still be supported. Maintenance and bug fixes will still be applied. There will still be active development for the back- porting of new features introduced in Spirit v1.8.0 (and Spirit 1.9.0) to lesser able compilers; hopefully, fueled by contributions from the community. For instance, there is already a working AST tree back-port for VC6 and VC7 by Peder Holt.

This failure is caused by a compiler bug. Templated operators which combine different iterators built with iterator_facade or iterator_adaptor be present in an overload set even when those iterators are not interoperable. The usual result is that error messages generated by illegal use of these operators will be of lower quality. This failure is caused by a compiler bug. is_convertible<T,U>::value may be true for unrelated iterators T and U (including many of the Boost specialized adaptors) which use enable_if_convertible to restrict the applicability of converting constructors, even when T is not convertible to U because instantiating the conversion will cause a compilation failure. This test ensures the inclusion property of interval arithmetic is available for built-in floating-point types float and double. If the test fails, interval<float> and interval<double> should not be used on this compiler/platform since there will be no numerical guarantee. The failure is caused by standard library deficiencies -- it lacks basic_string class and the <locale> header. The failures are caused by problems with std::locale implementation The test fails at runtime for unknown reason The failures are caused by compiler bug: it's not possible to explicitly pass template arguments to member template function. The failure is serious and makes one of the primary interfaces unusable. This test fails only intermittently. The failure is caused by a problem in Boost code. The Boost developer is aware of the problem and plans to fix it. The failure is caused by a compiler bug. The failure is caused by a compiler bug, which has been reported to the compiler supplier (or is already known to them). The failure is caused by a standard library bug. The failure is caused by a standard library bug, which has been reported to the standard library supplier (or is already known to them). The failure is probably caused by the test code, harness, or configuration. Thus it may not affect users of the library. The failure is serious and likely to prevent all use of this Boost library with this compiler. The failure is serious and likely to prevent all use of this Boost library with this compiler. The failure is caused by a compiler bug, which has been reported to the compiler supplier (or is already known to them). The failure is caused by a platform API bug. The failure is caused by a platform API bug, which has been reported to the platform API supplier (or is already known to them). The failure is not serious and will not affect most users. The library degrades gracefully. This compiler's bugs are not supported by the library.