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This article introduces the knowledge of "Why do not make unlimited non-member function calls in C++". Many people will encounter such a dilemma in the operation of actual cases. next, let the editor lead you to learn how to deal with these situations! I hope you can read it carefully and be able to achieve something!

T.69: within the template, do not make unrestricted non-member function calls unless you want it to be a customization point

Reason (reason)

Provide only intended flexibility.

Provide flexibility only as intended.

Avoid vulnerability to accidental environmental changes.

Avoid the vulnerability of accidental environmental changes.

Example (sample)

There are three major ways to let calling code customize a template.

There are three main ways for calling code to customize templates.

Template

/ / Call a member function

Void test1 (T t)

{

T.F (); / / require T to provide f ()

}

Template

Void test2 (T t)

/ / Call a non-member function without qualification

{

F (t); / / require f (/ * tasking /) be available in caller's scope or in T's namespace

}

Template

Void test3 (T t)

/ / Invoke a "trait"

{

Test_traits::f (t); / / require customizing test_traits

/ / to get non-default functions/types

}

A trait is usually a type alias to compute a type, a constexpr function to compute a value, or a traditional traits template to be specialized on the user's type.

A feature is usually a type alias for evaluating a type, a constant expression function for evaluation, or a traditional feature template that is specialized for a user type.

Note (Note)

If you intend to call your own helper function helper (t) with a value t that depends on a template type parameter, put it in a:: detail namespace and qualify the call as detail::helper (t) An unqualified call becomes a customization point where any function helper in the namespace of t's type can be invoked; this can cause problems like unintentionally invoking unconstrained function templates.

If you want to call your own helper function helper (t) with a value that depends on template type parameters, put it into:: detail namespace and use detail::helper (t) to qualify the call; if a helper function is in a namespace where the type of t can be triggered, unrestricted calls will become a customized point; this will cause unexpected calls to unconstrained function templates and other problems.

Enforcement (implementation recommendations)

In the same namespace of the template, if there is a non-member function with the same name, the unrestricted call in the tag template for the non-member function that passes variables of the affected type

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