CS253: Software Development with C++
Spring 2018
Duck Typing
🦆
🙶If it walks like a duck,
and quacks like a duck,
then it’s a duck.🙷
This is an old common-sense saying that stresses functionality over formal definition. If I were doing 200mph on I-25 in Luke Skywalker’s speeder, I wouldn’t get far claiming that it’s “not a car”. The law would probably view it as a car, even though it has no wheels.
A vector requires that its stored type be copyable, both via copy ctor and
assignment operator. For example, you can have a vector<string>,
because strings are copyable
string now = "2024-04-20T02:13:58"; // ISO 8601, baby! vector<string> v; v.push_back(now); cout << v.front() << '\n';
2024-04-20T02:13:58
How about a non-copyable class?
vector<istream> v; cout << "size=" << v.size() << endl;
size=0
vector<istream> v; v.push_back(cin);
In file included from /usr/include/c++/8/x86_64-redhat-linux/bits/c++allocator.h:33,
from /usr/include/c++/8/bits/allocator.h:46,
from /usr/include/c++/8/string:41,
from /usr/include/c++/8/bits/locale_classes.h:40,
from /usr/include/c++/8/bits/ios_base.h:41,
from /usr/include/c++/8/ios:42,
from /usr/include/c++/8/istream:38,
from /usr/include/c++/8/sstream:38,
from /usr/include/c++/8/complex:45,
from /usr/include/c++/8/ccomplex:39,
from /usr/include/c++/8/x86_64-redhat-linux/bits/stdc++.h:52,
from c.cc:1:
/usr/include/c++/8/ext/new_allocator.h: In instantiation of 'void __gnu_cxx::new_allocator<_Tp>::construct(_Up*, _Args&& ...) [with _Up = std::basic_istream<char>; _Args = {const std::basic_istream<char, std::char_traits<char> >&}; _Tp = std::basic_istream<char>]':
/usr/include/c++/8/bits/alloc_traits.h:475: required from 'static void std::allocator_traits<std::allocator<_CharT> >::construct(std::allocator_traits<std::allocator<_CharT> >::allocator_type&, _Up*, _Args&& ...) [with _Up = std::basic_istream<char>; _Args = {const std::basic_istream<char, std::char_traits<char> >&}; _Tp = std::basic_istream<char>; std::allocator_traits<std::allocator<_CharT> >::allocator_type = std::allocator<std::basic_istream<char> >]'
/usr/include/c++/8/bits/stl_vector.h:1079: required from 'void std::vector<_Tp, _Alloc>::push_back(const value_type&) [with _Tp = std::basic_istream<char>; _Alloc = std::allocator<std::basic_istream<char> >; std::vector<_Tp, _Alloc>::value_type = std::basic_istream<char>]'
c.cc:2: required from here
/usr/include/c++/8/ext/new_allocator.h:136: error: use of deleted function
'std::basic_istream<_CharT, _Traits>::basic_istream(const
std::basic_istream<_CharT, _Traits>&) [with _CharT = char; _Traits =
std::char_traits<char>]'
