Both foo() and bar() can only be assigned to func_ptr2. ยง8.3.6/2: A default argument is not part of the type of a function. [Example: int f(int = 0); void h() { int j = f(1); int k = f(); // OK, means f(0) } int (*p1)(int) = &f; int (*p2)() = &f; // error: type … Read more
The default argument applies to the specialization — and, in fact, a specialization must accept (so to speak) the base template’s default argument(s). Attempting to specify a default in the specialization: template<class A = int, class B=double> class Base {}; template<class B=char> // … …is an error. Likewise, if we change the specialization so that … Read more
def my_func(working_list=None): if working_list is None: working_list = [] # alternative: # working_list = [] if working_list is None else working_list working_list.append(“a”) print(working_list) The docs say you should use None as the default and explicitly test for it in the body of the function.
The alternative would be quite heavyweight — storing “default argument values” in the function object as “thunks” of code to be executed over and over again every time the function is called without a specified value for that argument — and would make it much harder to get early binding (binding at def time), which … Read more
In the first one, a temporary std::string is initialised from the literal “Unnamed” each time the function is called without an argument. In the second case, the object defaultName is initialised once (per source file), and simply used on each call.
You can’t typehint strings, you can only typehint objects and arrays, so this is incorrect: function setName ( string $name = “happ”) { (The reason you don’t get a compile-time error here is because PHP is interpreting “string” as the name of a class.) The wording in the docs means that if you do this: … Read more
You can define a companion object for your data class and overload its invoke operator to use default values when null is passed: data class Data private constructor( val name: String, val number: Long ) { companion object { operator fun invoke( name: String? = null, number: Long? = null ) = Data( name ?: … Read more
It’s written as: def my_function(self, param_one=None): # Or custom sentinel if None is vaild if param_one is None: param_one = self.one_of_the_vars And I think it’s safe to say that will never happen in Python due to the nature that self doesn’t really exist until the function starts… (you can’t reference it, in its own definition … Read more
The default argument applies to the specialization — and, in fact, a specialization must accept (so to speak) the base template’s default argument(s). Attempting to specify a default in the specialization: template<class A = int, class B=double> class Base {}; template<class B=char> // … …is an error. Likewise, if we change the specialization so that … Read more
It does work, but only in Python 3. See PEP 3102. From glancing over the “what’s new” documents, it seems that there is no 2.x backport, so you’re out of luck. You’ll have to accept any keyword arguments (**kwargs) and manually parse it. You can use d.get(k, default) to either get d[k] or default if … Read more