[rust-dev] Polymorphism & default parameters in rust

Patrick Walton pwalton at mozilla.com
Sat Aug 4 12:10:57 PDT 2012

On 08/04/2012 11:58 AM, Daniel Patterson wrote:
> You get the default param behavior, without the magic of overloading,
> and it is clear from application what you are doing. This costs one
> line of code, and having a separate name for the defaulted version…

Yes. This should be plan A for Rust programmers; plan B is method 
chaining :)

As an aside, the prevailing Rust style is clarity over cleverness, even 
if that results in a little less flexibility. For example, our map 
function in the standard library isn't as flexible as it could be; you 
can't map from a mutable vector to an immutable one or from an immutable 
vector to a mutable one with one function. Scala's map function does let 
you do that, and we could conceivably have duplicated that functionality 
with traits. But we really wanted the signature of the map function to be:

     fn map<T,U>(v: [T], f: &fn(T)->U) -> [U]

Instead of something more complicated.

As for named and optional parameters, I'm not opposed to them if they 
prove necessary, but my thinking right now is that they're not a version 
1.0 feature.


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