From http://www.boost.org/doc/libs/1_37_0/libs/bind/bind.html#Synopsis :

namespace { unspecified-placeholder-type-1 _1; unspecified-placeholder-type-2 _2; unspecified-placeholder-type-3 _3; // implementation defined number of additional placeholder definitions } Then I use placeholders like this: class X { void h(int); void f1() { return boost::bind(&X::h, this, _1)(3); } } As f1 is inline, it should be the same in all the translation units, to obey ODR. However, anonyomous namespace is different in a different translation unit, so _1 is different variable. Is One Definition Rule broken ?