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## Portability

`BOOST_FOREACH` uses some fairly sophisticated techniques that not all compilers support. Depending on how compliant your compiler is, you may not be able to use `BOOST_FOREACH` in some scenarios. Since `BOOST_FOREACH` uses Boost.Range, it inherits Boost.Range's portability issues. You can read about those issues in the Boost.Range Portability section.

In addition to the demands placed on the compiler by Boost.Range, `BOOST_FOREACH` places additional demands in order to handle rvalue sequences properly. (Recall that an rvalue is an unnamed object, so an example of an rvalue sequence would be a function that returns a `std::vector<>` by value.) Compilers vary in their handling of rvalues and lvalues. To cope with the situation `BOOST_FOREACH` defines three levels of compliance, described below:

Table 5.1. BOOST_FOREACH Compliance Levels

Level | Meaning
--- | ---
Level 0 | Highest level of compliance `BOOST_FOREACH` works with lvalues, rvalues and const-qualified rvalues.
Level 1 | Moderate level of compliance `BOOST_FOREACH` works with lvalues and plain rvalues, but not const-qualified rvalues. `BOOST_FOREACH_NO_CONST_RVALUE_DETECTION` is defined in this case.
Level 2 | Lowest level of compliance `BOOST_FOREACH` works with lvalues only, not rvalues. `BOOST_FOREACH_NO_RVALUE_DETECTION` is defined in this case.

Below are the compilers with which `BOOST_FOREACH` has been tested, and the compliance level `BOOST_FOREACH` provides for them.

Table 5.2. Compiler Compliance Level

Compiler | Compliance Level
--- | ---
Visual C++ 8.0 | Level 0
Visual C++ 7.1 | Level 0
Visual C++ 7.0 | Level 2
Visual C++ 6.0 | Level 2
gcc 4.0 | Level 0
gcc 3.4 | Level 0
gcc 3.3 | Level 0
mingw 3.4 | Level 0
Intel for Linux 9.0 | Level 0
Intel for Windows 9.0 | Level 0
Intel for Windows 8.0 | Level 1
Intel for Windows 7.0 | Level 2
Comeau 4.3.3 | Level 0
Borland 5.6.4 | Level 2
Metrowerks 9.5 | Level 1
Metrowerks 9.4 | Level 1
SunPro 5.8 | Level 2
qcc 3.3 | Level 0
tru64cxx 65 | Level 2
tru64cxx 71 | Level 2