CODEWITHSUNDEEP
c++templatestypestypename
Yippie-Ki-Yay
Yippie-Ki-Yay

Reputation: 22854

Template typename

Does the C++ standard somehow specify what can a T be in the following declaration:

template <typename T>

I mean, from practical terms of view this can be any particular type, which allows the template to compile (when the corresponding substitution happens).

But what about the strict definition?

Upvotes: 0

Views: 667

Answers (4)

Cort Ammon
Cort Ammon

Reputation: 10903

boost has a helpful template, enable_if that lets you enable templates for only particular types.

Upvotes: 0

Kiril Kirov
Kiril Kirov

Reputation: 38193

As you want the standard, here it is:

C++03, 14.1, Template parameters:

A template defines a family of classes or functions.

template-declaration:
    exportopt template < template-parameter-list > declaration
template-parameter-list:
    template-parameter
     template-parameter-list , template-parameter

template-parameter:
    type-parameter
    parameter-declaration
type-parameter:
    class identifieropt
    class identifieropt = type-id
    typename identifieropt
    typename identifieropt = type-id
    template < template-parameter-list > class identifieropt
    template < template-parameter-list > class identifieropt = id-expression

..

A type-parameter defines its identifier to be a type-name (if declared with class or typename) or template-name (if declared with template) in the scope of the template declaration.

..

If the use of a template-argument gives rise to an ill-formed construct in the instantiation of a template specialization, the program is ill-formed.

The other things are for default parameters, non-type templates, etc. In other words, the standard does not say anything about T.

Upvotes: 2

Chris
Chris

Reputation: 12201

There is no strict definition, since that would seem to go against the very purpose of templates. T is any type that is, for example, passed as an argument to a function with a parameter of type T.

You sacrifice the safety of strict type definitions for the code reusability of templates. With that freedom, you need to provide the checks to make sure that T is of a reasonable type for the function.

Upvotes: 0

Joshua Clark
Joshua Clark

Reputation: 1356

It is the responsibility of the programmer to ensure that the data type being used for T is compatible and has all the necessary operations that will performed on T defined. As far as the C++ standard is concerned any data type can be used in place of T there.

Upvotes: 1

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