[temp.deduct.conv]
13 Templates [temp]
13.10 Function template specializations [temp.fct.spec]
13.10.3 Template argument deduction [temp.deduct]
13.10.3.4 Deducing conversion function template arguments [temp.deduct.conv]
If P is a reference type, the type referred to by P is used in place of P for type deduction and for any further references to or transformations of P in the remainder of this subclause.
If A is not a reference type:
- If P is an array type, the pointer type produced by the array-to-pointer standard conversion is used in place of P for type deduction; otherwise,
- If P is a function type, the pointer type produced by the function-to-pointer standard conversion is used in place of P for type deduction; otherwise,
- If P is a cv-qualified type, the top-level cv-qualifiers of P's type are ignored for type deduction.
If A is a cv-qualified type, the top-level cv-qualifiers of A's type are ignored for type deduction.
If A is a reference type, the type referred to by A is used for type deduction.
In general, the deduction process attempts to find template argument values that will make the deduced A identical to A.
However, certain attributes of A may be ignored:
If the original A is a reference type, any cv-qualifiers of A (i.e., the type referred to by the reference).
If the original A is a function pointer or pointer-to-member-function type with a potentially-throwing exception specification ([except.spec]), the exception specification.
Any cv-qualifiers in A that can be restored by a qualification conversion.
These attributes are ignored only if type deduction would otherwise fail.
If ignoring them allows more than one possible deduced A, the type deduction fails.