249. Return Type of auto_ptr::operator=

Section: 99 [auto.ptr] Status: NAD Submitter: Joseph Gottman Opened: 2000-06-30 Last modified: 2016-02-10

Priority: Not Prioritized

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Discussion:

According to section 20.4.5, the function auto_ptr::operator=() returns a reference to an auto_ptr. The reason that operator=() usually returns a reference is to facilitate code like

    int x,y,z;
    x = y = z = 1;

However, given analogous code for auto_ptrs,

    auto_ptr<int> x, y, z;
    z.reset(new int(1));
    x = y = z;

the result would be that z and y would both be set to NULL, instead of all the auto_ptrs being set to the same value. This makes such cascading assignments useless and counterintuitive for auto_ptrs.

Proposed resolution:

Change auto_ptr::operator=() to return void instead of an auto_ptr reference.

Rationale:

The return value has uses other than cascaded assignments: a user can call an auto_ptr member function, pass the auto_ptr to a function, etc. Removing the return value could break working user code.