TSa wrote: > The use of £ in > > sub foo (£ pointlike ::PointType $p1, PointType $p2 --> PointType) > > is that of *structural* subtyping. Here FoxPoint is found to be > pointlike. In that I would propose again to take the 'like' operator > from JavaScript 2. Doing that the role should be better named Point > and foo reads: > > sub foo (like Point ::PointType $p1, PointType $p2 --> PointType) > > This is very useful to interface between typed and untyped code. > With the 'like' the role Point has to be *nominally* available > in the argument. There's no problem with 'like'-types being more > expensive than a nominal check.
Ah; that clears things up considerably. If I understand you correctly, John is using '£' to mean "use Duck Typing here". _That_, I can definitely see uses for. As well, spelling it as 'like' instead of '£' is _much_ more readable. With this in mind, the above signature reads as "$p1 must be like a Point, but it needn't actually be a Point. Both $p2 and the return value must be the same type of thing that $p1 is." What, if anything, is the significance of the fact that pointlike (in John's example; 'Point' in TSa's counterexample) is generic? -- Jonathan "Dataweaver" Lang
