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JohnnyCode

what is a template from c++ intent?

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JohnnyCode    1046

I wonder what is a template issued compiler object, is it one of the two following alternatives- and if yes- could you elaborate on anything of the one of the definitions alternatives it misses?

 

A template type of a variable in c++ compiling protocol is :

 

1 alternative : a variable of any type without any compiler ability to check validity of instructions with it?

 

2 alternative : a type of objects that share certain properties and the writer of code wishes to implement unified commands over them without need to derive them from common ancesting object in a strongly types language?

 

or both of them are totaly wrong?

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jwezorek    2663

Neither is really correct but 2 is closer to correct; 1 sounds more like a C-style macro.

 

Basically you can think of templates as type-safe macros. This is not altogether accurate but is a good first approximation.

 

In other words both macros and templates cause code to get generated. The compiler will do some work for you filling in what you mean. However, in the case macros the way that the preprocessor does this code generation is completely braindead: it doesn't know anything about the types involved it just pastes the arguments into the macro and if what comes out is garbage then so be it.

 

In the case of templates the compiler is checking types while it is doing the code generation.

Edited by jwezorek

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JohnnyCode    1046

but macro is just a missplaced continuing code with ability to replace in many places. Template is not. Wtf is template sad.png I am lost never needed to use it, never wished to use it, but I have been in an enviroment where it was a principle to get used. Isn't it just dangerous? As you said, the second alternative is quite close, so it allows one to implement instructions upon objects that do not share ancestors, are being of different types with certain matches, but share possible instructions validity in manner of members. But tamplates for me are such a thin ice.

 

Never ever I have used it actualy. What is it intended exactly for? The second alternative is the only best stuff I could come up with, but it opens missinterpretation that compiler cannot catch, making one's issues more difficult?

Edited by JohnnyCode

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SeanMiddleditch    17565

I am lost never needed to use it, never wished to use it, but I have been in an enviroment where it was a principle to get used. Isn't it just dangerous?


Search for "generic programming." They're super useful, by far the most important missing feature from any language that lacks them (C, Go, etc.).

The easy example in C++ is a std::vector or std::unique_ptr. It would totally suck to have to reimplement those over and over and over again for every type.

so it allows one to implement instructions upon objects that do not share ancestors


That is not a bad thing. Needing ancestor types to do things is _bad_, not good.

That said, C++17 (or around then) will have this thing called Concepts which are a way of constraining templates to only works on types that conform to a specific contract (without being forced to add ancestor types).

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Bacterius    13165


Frob, did you ever fall for tamplate usage, or sticked to conforming compiler runtime code? You sure did Frob. Template= utopia!!! IT DOES

 

You.. do realize that templates are part of the language, right?

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Ectara    3097


standard vectors just poses pointers. Right? Nothing further and they do not mess with a template stuff.

Examine your compiler's included headers, and Ctrl+F/grep for "template". A five minute examination would have dispelled your counter-argument.

 

Another good use of generic programming is extensibility. Code that is templated can be used later in a way that the original coder had yet to conceive by substituting new types and values in place of the template parameters.

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JohnnyCode    1046

 

std::vector _is_ a template. That's why you use it like:
 
std::vector<int> foo;The `<int>` bit is a clear sign that you're instantiating the `std::vector` class template over the `int` type parameter.

 

Yes, you are right, I have never noticed std::vector can interleave objects, not only pointers. I avoided std:: lib always and its vectors.

 

I have coded a pooled memory manager. And I wonder whaether I should do it with a template or with just sizeof operator as I currently have. My point is wheather the template - if not needed- does have a runtime performance impact, or no runtime impact at all.

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