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Section: 99 [depr.lib.binders] Status: CD1 Submitter: Andrew Demkin Opened: 2002-04-26 Last modified: 2016-01-28
Priority: Not Prioritized
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Discussion:
The definition of bind1st() (99 [depr.lib.binders]) can result in the construction of an unsafe binding between incompatible pointer types. For example, given a function whose first parameter type is 'pointer to T', it's possible without error to bind an argument of type 'pointer to U' when U does not derive from T:
foo(T*, int);
struct T {};
struct U {};
U u;
int* p;
int* q;
for_each(p, q, bind1st(ptr_fun(foo), &u)); // unsafe binding
The definition of bind1st() includes a functional-style conversion to map its argument to the expected argument type of the bound function (see below):
typename Operation::first_argument_type(x)
A functional-style conversion (99 [depr.lib.binders]) is defined to be semantically equivalent to an explicit cast expression (99 [depr.lib.binders]), which may (according to 5.4, paragraph 5) be interpreted as a reinterpret_cast, thus masking the error.
The problem and proposed change also apply to 99 [depr.lib.binders].
Proposed resolution:
Add this sentence to the end of 99 [depr.lib.binders]/1:
"Binders bind1st and bind2nd are deprecated in
favor of std::tr1::bind."
(Notes to editor: (1) when and if tr1::bind is incorporated into the standard, "std::tr1::bind" should be changed to "std::bind". (2) 20.5.6 should probably be moved to Annex D.
Rationale:
There is no point in fixing bind1st and bind2nd. tr1::bind is a superior solution. It solves this problem and others.