Use arrays : function test($options = array()) { $defaults = array( ‘t1’ => ‘test1’, ‘t2’ => ‘test2’, ‘t3’ => ‘test3’, ); $options = array_merge($defauts, $options); extract($options); echo “$t1, $t2, $t3”; } Call your function this way : test(array(‘t3’ => ‘hi, i am different’));
Not directly, but you might be able to do something with std::bind: int func(int arg1 = 0, int arg2 = 0, int arg3 = 0); // elsewhere… using std::bind; using std::placeholders::_1; auto f = bind(func, 0, _1, 0); int result = f(3); // Call func(0, 3, 0); The downside is of course that you are … Read more
You can’t really define this as the default value, since the default value is evaluated when the method is defined which is before any instances exist. The usual pattern is to do something like this instead: class C: def __init__(self, format): self.format = format def process(self, formatting=None): if formatting is None: formatting = self.format print(formatting) … Read more
That code would work if in the very first declaration of the function, the last parameter has default value, something like this: //declaration void error(char const *msg, bool showKind, bool exit = false); And then in the same scope you can provide default values for other arguments (from right side), in the later declaration, as: … Read more
The first form can be made to work, by adding a deduction guide: template <typename… Ts> struct debug { debug(Ts&&… ts, const std::source_location& loc = std::source_location::current()); }; template <typename… Ts> debug(Ts&&…) -> debug<Ts…>; Test: int main() { debug(5, ‘A’, 3.14f, “foo”); } DEMO
You can use it to cache values between function calls: def get_from_cache(name, cache={}): if name in cache: return cache[name] cache[name] = result = expensive_calculation() return result but usually that sort of thing is done better with a class as you can then have additional attributes to clear the cache etc.
In C++03, the specification explicitly prohibits the default argument from being used to deduce a template argument (C++03 ยง14.8.2/17): A template type-parameter cannot be deduced from the type of a function default argument. In C++11, you can provide a default template argument for the function template: template <typename T = float> void bar(int a, T … Read more
Default parameter values must appear on the declaration, since that is the only thing that the caller sees. EDIT: As others point out, you can have the argument on the definition, but I would advise writing all code as if that wasn’t true.
You can’t really define this as the default value, since the default value is evaluated when the method is defined which is before any instances exist. The usual pattern is to do something like this instead: class C: def __init__(self, format): self.format = format def process(self, formatting=None): if formatting is None: formatting = self.format print(formatting) … Read more