On Tue, Jul 30, 2019 at 8:31 PM <alan.f...@gmail.com> wrote:
> My suggestion was that you can't use a pointer type as a type parameter if
> the latter is subject to a contract.
>
I'm not sure I understand you. Wouldn't that preclude using a generic map
with pointers as keys?
> In the case you mention, the contract could be expressed as a disjunction
> of value and pointer methods:
>
> contract stringer(T) {
> T String() string, *T String() string
> }
>
Currently, Disjunctions only apply to a single type. You can't form
expressions like this.
IMO that's a good restriction to maintain. Because the more powerful the
contract language becomes, the harder it'll be to make it useful.
> On the other hand and more generally, not knowing whether the type
> parameter represented a pointer or a value might lead to some awkward
> coding. For example, you wouldn't be able to de-reference the type argument
> as it might not be a pointer.
>
If a generic function wants to de-reference an argument, it should specify
that as a pointer: func f(type T) (p *T)
This is the same as with slices, maps, channels, functions or any composite
type - you can't express "type parameter T should be a slice of some kind",
because you are instead expected to just specify []T if you want a slice.
>
> It's clearly an area where some more thought is needed as Ian intimated
> earlier.
>
> Alan
>
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