- Function type syntax confusion - 2 Updates
- Reproducing a sequence from a binary tree... - 1 Update
- [Jesus Loves You] Messages of hope and a future - 1 Update
| Juha Nieminen <nospam@thanks.invalid>: May 31 04:13PM It's still unclear to me what the difference is between the function type syntax of the form "ReturnType(*)(ParameterTypes)" and "ReturnType(ParameterTypes)". Sometimes they seem to be interchangeable, sometimes they don't. For example, this is valid: //------------------------------------------- using F1 = int(*)(int); using F2 = int(int); void foo1(F1 funcPtr); // ok void foo2(F2 funcPtr); // ok //------------------------------------------- However, this is not valid: //------------------------------------------- F1 funcPtr1 = someFunc; // ok F2 funcPtr2 = someFunc; // error //------------------------------------------- Likewise: //------------------------------------------- std::function<int(int)> funcObj1; // ok std::function<int(*)(int)> funcObj2; // error std::set<int, bool(*)(int, int)> set1; // ok std::set<int, bool(int, int)> set2; // error //------------------------------------------- So they are like the reverse of each other. F2 above can be used for a function declaration, which might give some insight into what it means. In other words: //------------------------------------------- F2 someFunction; // ok int main() { int value = someFunction(5); // ok. } int someFunction(int v) { return v+1; } //------------------------------------------- |
| Ben Bacarisse <ben.usenet@bsb.me.uk>: May 31 05:49PM +0100 > It's still unclear to me what the difference is between the function type > syntax of the form "ReturnType(*)(ParameterTypes)" and > "ReturnType(ParameterTypes)". The first is a pointer type and the second a function type. > using F2 = int(int); > void foo1(F1 funcPtr); // ok > void foo2(F2 funcPtr); // ok Because functions can't be passed as parameters, function types are converted to pointer-to-function types in this context. This is annoying, but it's hang-over from C. It's analogous to (raw) array types in parameter lists -- they also get converted to pointer types. > F1 funcPtr1 = someFunc; // ok > F2 funcPtr2 = someFunc; // error > //------------------------------------------- And you can't assign to a function. > //------------------------------------------- > std::function<int(int)> funcObj1; // ok > std::function<int(*)(int)> funcObj2; // error You need a function type, not a pointer type, for std::function. > std::set<int, bool(int, int)> set2; // error > //------------------------------------------- > So they are like the reverse of each other. A set hold data objects, and pointers are data objects so a set of pointers makes sense. Functions are not considered to be data objects in either C or C++ so you can't put them into collections. > insight into what it means. In other words: > //------------------------------------------- > F2 someFunction; // ok Yes, F2 is a function type and can be used to declare (but not define) functions. -- Ben. |
| "Alf P. Steinbach" <alf.p.steinbach+usenet@gmail.com>: May 27 12:26PM +0200 On 27.05.2020 01:52, Chris M. Thomasson wrote: > Basically. However, I want to extend this to handle higher bases. Right > how its only a 2-ary tree. It can be extended to n-ary. The code is down > right crude and very basic for now. Oh look, an efficient integral power function: namespace impl { constexpr inline auto intpow( const double base, const int exponent ) -> double { double result = 1; double weight = base; for( int n = exponent; n != 0; weight *= weight ) { if( is_odd( n ) ) { result *= weight; } n /= 2; } return result; } } // namespace impl /// @endcond /// \brief Efficient *x* to the *n*'th power, when *n* is an integer. /// /// \param base The *x* in "*x* to the *n*'th". /// \param exponent The *n* in "*x* to the *n*'th". /// /// Essentially this is Horner's rule adapted to calculating a power, so that the /// number of floating point multiplications is at worst O(log2(n)). constexpr inline auto intpow( const double base, const int exponent ) -> double { return (0?0 : exponent == 0? 1.0 : exponent < 0? 1.0/impl::intpow( base, -exponent ) : impl::intpow( base, exponent ) ); } <url: https://github.com/alf-p-steinbach/cppx-core-language/blob/master/source/cppx-core-language/calc/floating-point-operations.hpp> [snip] - Alf |
| Juha Nieminen <nospam@thanks.invalid>: May 27 06:35AM > [Jesus Loves You] Messages of hope and a future You may get a sense of martyrdom and righteous victimhood when you keep spamming this newsgroup with provocative off-topic content and getting negative reactions. However, even if your god were real and exactly like you believe him to be, even he wouldn't approve of you behaving like this. I think that even he would rebuke you for this kind of disruptive behavior. He would not be pleased with you. I don't think even he would want you to spread his word in this manner. The fact that you don't accept that makes you an obsessed bigot. |
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