Regex ICU support doesn't compile with #define U_USING_ICU_NAMESPACE 0

[Matthias Schiffer <matthias@…>]

To prevent namespace pollution, I definde U_USING_ICU_NAMESPACE to 0 in my projects before including any ICU headers. This prevents the ICU headers from adding a "using namespace icu" to the root namespace, so classes like UnicodeString are only available in the icu:: namespace.

While most uses of ICU classes in the Boost Regex ICU headers are prepended with U_NAMESPACE_QUALIFIER (e.g. Locale and Collator), this seems to have been forgotten for UnicodeString, causing the compile to fail.

Minimal example to reproduce and patch attached.

[Matthias Schiffer <matthias@…>]

Minimal example

[Matthias Schiffer <matthias@…>]

Patch

[John Maddock]

(In [57739]) Suppress external templates with Mingw32 - it seems to cause issues with dll's. Fix match_results.swap. Add missing namespace qualifiers to ICU code: fixes #3631.