std::remove_const with const references

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std::remove_const removes top level const-qualifications. In const T&, which is equivalent to T const&, the qualification is not top-level: in fact, it does not apply to the reference itself (that would be meaningless, because references are immutable by definition), but to the referenced type.

Table 52 in Paragraph 20.9.7.1 of the C++11 Standard specifies, regarding std::remove_const:

The member typedef type shall name the same type as T except that
any top-level const-qualifier has been removed.
[ Example: remove_const<const volatile int>::type evaluates to
volatile int, whereas remove_const<const int*>::type evaluates
to const int*. — end example ]

In order to strip const away, you first have to apply std::remove_reference, then apply std::remove_const, and then (if desired) apply std::add_lvalue_reference (or whatever is appropriate in your case).

NOTE: As Xeo mentions in the comment, you may consider using an alias template such as Unqualified to perform the first two steps, i.e. strip away the reference, then strip away the const– (and volatile-) qualification.

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