The conversion context classes manage internal, per-thread stacks of conversion context instances. A conversion context constructor pushes a reference to the new instance onto the appropriate conversion context stack(s). A destructor pops the instance off the stack(s). The top-level element of a stack defines the conversion context currently in effect for all implicit conversions.

The current conversion context remains in effect until either a new conversion context instance is constructed, or until it goes out of scope and is destroyed. Note that the current conversion context also applies within any functions called from the block where the context was created.