non-dependent name in template function

This is a discussion on non-dependent name in template function within the C++ Programming forums, part of the General Programming Boards category; Hello everyone, I am confused about what Bjarne means below, and I quoted the section name, his words and his ...

  1. #1
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    non-dependent name in template function

    Hello everyone,


    I am confused about what Bjarne means below, and I quoted the section name, his words and his sample.

    My question is, what did he mean "A call that by coincidence has an argument that matches an actual template parameter type is not dependent"?

    I think the compile error is because, g (1) function call is not dependent on template parameter, and it should be resolved in the definition phase (not instantiation phase) of template function f. But in definition phase of f, what g is (the symbol g) can not be resolved. So comes the compile error.

    Is my analysis correct? What did Bjarne mean?

    (section C.13.8.1 Dependent Names)

    --------------------
    A call that by coincidence has an argument that matches an actual template parameter type is not dependent. For example,
    --------------------

    Code:
    template <class T> T f (T a)
    {
    	return g (1); // error: no g() in scope and g(1) doesn't depent on T
    }
    
    int g (int);
    
    int z = f (2);

    thanks in advance,
    George

  2. #2
    Cat without Hat CornedBee's Avatar
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    Yes, that's correct.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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    Thanks CornedBee,


    One of the original questions is not answered. :-)

    What do you think Bjarne means in the following statements along with the sample code? What is "A call that by coincidence"? and "an argument that matches an actual template parameter type is not dependent"? Could you let me know how they reflect in the sample code please?

    --------------------
    A call that by coincidence has an argument that matches an actual template parameter type is not dependent. For example,
    --------------------

    Quote Originally Posted by CornedBee View Post
    Yes, that's correct.

    regards,
    George

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    Captain Crash brewbuck's Avatar
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    Quote Originally Posted by George2 View Post
    What do you think Bjarne means in the following statements along with the sample code? What is "A call that by coincidence"? and "an argument that matches an actual template parameter type is not dependent"? Could you let me know how they reflect in the sample code please?
    It just means that just because g() takes an int, and T happens to be int, that doesn't magically cause g() to be a dependent name. It's only dependent if T, or another dependent type, occurs in g().

  5. #5
    Cat without Hat CornedBee's Avatar
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    occurs in g()
    That would be the call to g(), mind you, not the definition.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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    Thanks brewbuck,


    I have got your idea.

    Quote Originally Posted by brewbuck View Post
    It just means that just because g() takes an int, and T happens to be int, that doesn't magically cause g() to be a dependent name. It's only dependent if T, or another dependent type, occurs in g().

    Thanks CornedBee,


    Quote Originally Posted by CornedBee View Post
    That would be the call to g(), mind you, not the definition.
    What do you mean above? Could you show some pseudo code please?


    regards,
    George

  7. #7
    Cat without Hat CornedBee's Avatar
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    Of you understood what brewbuck said, you don't need clarification of what I said.
    All the buzzt!
    CornedBee

    "There is not now, nor has there ever been, nor will there ever be, any programming language in which it is the least bit difficult to write bad code."
    - Flon's Law

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    Thanks CornedBee,


    Question answered.

    Quote Originally Posted by CornedBee View Post
    Of you understood what brewbuck said, you don't need clarification of what I said.

    regards,
    George

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