Optional function arguments

[farnz]

Just to help avoid going over old ground, the following discussions all appear relevant:

An approach to resolving some issues with optional arguments

Some issues in implementing optional arguments have been: Implicitly calling expensive new functions to construct the defaults Calling the right drop method My proposal is to restrict the default values for optional parameters to be Copy. This would make it cheap to construct defaults and trivial to drop. This approach would rule out having a Vec or Option<Vec<_>> as an optional argument. However, allowing default arguments for copy types would still be very useful. Types for Enum Variants, …

Doesn't support named arguments

I would like to be able to specify named arguments for functions and methods. This will improve the readability and comprehension of the code. It seems that we can use positional arguments and arguments based on structures for now. However, I still do not quite understand why there is no such option now? Is this a special solution or just a functionality that has not yet been implemented? There is such an opinion that a flexible function should generally be implemented on the argument of structu…

Shorthand for `Default::default()`

Is there anyone proposed something similar to this? foo(v, ~, ~, 10); desugar to foo(v, <_ as Default>::default(), <_ as Default>::default(),10); Today with macros the best we can do is foo(v, d!(), d!(), 10); where d!() is defined as the above but since it is short it is likely to collide with definitions.

And a very similar syntax proposal is in Pre-RFC: make function arguments for Option-typed arguments - any proposal here should cover all the critiques made there.