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Using Allocator = typename vector::allocator_type Ĭ++ standard library types generally provide these member types to allow you to recover the template type arguments from the type. Using Value = typename vector::value_type

You might think you could rescue them by naming them and putting all the future nonsense in the variadic portion: templateĮrror C2977: 'std::vector': too many template argumentsĮrror: too many template arguments for class template 'vector'Įrror: too many arguments for class template "std::vector"įortunately, you can recover the Value and Allocator from std::vector because std::vector lets you access the underlying type and allocator through member types. Now, once we’ve accepted any kind of vector, we have lost the template parameters that name the value type and allocator. This works today, but it may not work tomorrow.Ī future version of std::vector might add new template arguments, provided that they have suitable defaults that preserve existing behavior.¹ We don’t want that future version to break us, so we should slurp up all the template arguments that exist: template But if somebody has a vector with a custom allocator, then your function won’t match. There is a second template argument for the allocator, which has a default value that nearly everyone uses. However, this does not actually accept any vector specialization. Your first try would probably be something like this: template Suppose you want to write a template function that accepts any specialization of std::vector.