haxe “should be int” error

问题

Haxe seems to assume that certain things must be Int. In the following function,

class Main {
    static function main() {
        function mult_s<T,A>(s:T,x:A):A { return cast s*x; }
        var bb = mult_s(1.1,2.2);
    }
}

I got (with Haxe 3.01):

Main.hx:xx: characters 48-49 : mult_s.T should be Int
Main.hx:xx: characters 50-51 : mult_s.A should be Int

Can anyone please explain why T and A should be Int instead of Float?

---

A more puzzling example is this:

class Main {
    public static function min<T:(Int,Float)>(t:T, t2:T):T { return t < t2 ? t : t2; }
    static function main() {
        var a = min(1.1,2.2); //compile error
        var b = min(1,2); //ok
    }
}

I can't see why t<t2 implies that either t or t2 is Int. But Haxe seems prefer Int: min is fine if called with Int's but fails if called with Float's. Is this reasonable?

Thanks,

回答1:

min<T:(Int,Float)> means T should be both Int and Float. See the constraints section of Haxe Manual.

Given Int can be converted to Float implicitly, you can safely remove the constraint of Int. i.e. the following will works:

http://try.haxe.org/#420bC

class Test {
  public static function min<T:Float>(t:T, t2:T):T { return t < t2 ? t : t2; }
  static function main() {
    var a = min(1.1,2.2); //ok
    $type(a); //Float
    trace(a); //1.1
    var b = min(1,2); //ok
    $type(b); //Int
    trace(b); //1
  }
}

来源：https://stackoverflow.com/questions/21518458/haxe-should-be-int-error