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// instantiates Blob<int> and the initializer_list<int> constructor
Blob<int> squares = {0,1,2,3,4,5,6,7,8,9};
// instantiates Blob<int>::size() const
for (size_t i = 0; i != squares.size(); ++i)
squares[i] = i*i; // instantiates Blob<int>::operator[](size_t)
instantiates the Blob<int> class and three of its member functions: operator[], size, and the initializer_list<int> constructor.
If a member function isn’t used, it is not instantiated. The fact that members are instantiated only if we use them lets us instantiate a class with a type that may not meet the requirements for some of the template’s operations (§ 9.2, p. 329).
By default, a member of an instantiated class template is instantiated only if the member is used.