Rectangle s(origin()); is a vexing parse too. It declares a function s which returns rectangle, and takes as argument pointer to function returning origin. Not sure what you meant by “works fine”. rectangle w( origin(), extents() ); declares a function w returning rectangle and taking arguments: pointer to function returning origin, and pointer to function … Read more
nothing at all, because X(answer); could be interpreted as the declaration of a variable. Your answer is hidden in here. If you declare a variable, you invoke its default ctor (if non-POD and all that stuff). On your edit: To get a temporary, you have a few options: (X(answer)); (X)answer; static_cast<X>(answer) X{answer}; (C++11) []{ return … Read more
is the concept of “most vexing parse” formally defined by the C++ standard. No. There is no concept of “most vexing parse” defined in the C++ standard. The standard does define the grammar from which the ambiguities arise, and it defines the rule that resolves the ambiguities, but it doesn’t name the ambiguities. According to … Read more
Case 1) m is interpreted as a function return my and taking no arguments. To see the expected output remove () i.e use my m; Case 2) This is something better known as the “Most vexing parse”. n is interpreted as a function returning my that takes an argument of type pointer to function returning … Read more
what does this syntax int(x) in the statement Foo f( int(x) ); mean? The parentheses around x are superfluous and will be ignored. So int(x) is the same as int x here, which means a parameter named x with type int. Is it the same as Foo f( int x );? Yes. Foo f( int(x) … Read more
Grouping. As a particular example, consider that you can declare a variable of function type such as int f(int); Now, how would you declare a pointer to such a thing? int *f(int); Nope, doesn’t work! This is interpreted as a function returning int*. You need to add in the parentheses to make it parse the … Read more
Nope. Your line Class object(); Declared a function. What you want to write is Class object; Try it out. You may also be interested in the most vexing parse (as others have noted). A great example is in Effective STL Item 6 on page 33. (In 12th printing, September 2009.) Specifically the example at the … Read more
istream_iterator<int>(cin) is exactly the same as istream_iterator<int> cin but with superfluous parens. This declarator syntax was inherited from C, and I think even the inventor of C (Ken Thompson?) described it as a mistake.
Let’s say MVP didn’t exist. How would you declare a function? A foo(); would be a variable definition, not a method declaration. Would you introduce a new keyword? Would you have a more awkward syntax for a function declaration? Or would you rather have A foo; define a variable and A foo(); declare a function? … Read more
This is due to the fact that TimeKeeper time_keeper(Timer()); is interpreted as a function declaration and not as a variable definition. This, by itself, is not an error, but when you try to access the get_time() member of time_keeper (which is a function, not a TimeKeeper instance), your compiler fails. This is how your compiler … Read more