[Boost-users] [Iterator][enable_if] Why use additional type for the enabler?

Subject: [Boost-users] [Iterator][enable_if] Why use additional type for the enabler?
From: Robert Jones (robertgbjones_at_[hidden])
Date: 2010-07-28 07:53:13

The iterator facade documention suggests that controlled conversion of
iterators
between const and mutable variants can be achieved by application of
enable_if.

Why does this need to involve an additional 'enabler' type, rather than
exploiting
the default void type of the enable_if template?

Thx,

- Rob.