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’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
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.
You are probably redefining the default parameter in the implementation of the function. It should only be defined in the function declaration. //bad (this won’t compile) string Money::asString(bool shortVersion=true){ } //good (The default parameter is commented out, but you can remove it totally) string Money::asString(bool shortVersion /*=true*/){ } //also fine, but maybe less clear as … Read more
NO,but there are some other options to implement default value. There are some good blog posts on the subject, but here are some specific examples. Option 1: The caller chooses to use default values // Both parameters are optional, use empty string for default value func Concat1(a string, b int) string { if a == … 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.