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Date: Fri, 07 Nov 2025 15:34:56 -0600
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Subject: Re: [PHP-DEV] Pre-RFC proposal: opt-in implicit interfaces / structural typing
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From: larry@garfieldtech.com ("Larry Garfield")

On Fri, Nov 7, 2025, at 1:19 PM, Rowan Tommins [IMSoP] wrote:
> On 07/11/2025 17:05, Spencer Malone wrote:
>> Hey all! Long time browser, first=C2=A0time emailer. I wanted to star=
t a=20
>> pre-RFC discussion on the proposal of opt-in implicit interfaces /=20
>> structural typing / "golang style interfaces".
>
>
> Hi and welcome :)
>
> In general, I prefer explicit code over implicit, so wouldn't be an=20
> enthusiastic supporter of this (although I might abstain rather than=20
> voting against).
>
> However, I though it worth mentioning that PHP has one implicit=20
> interface already: any class with an __toString() method magically=20
> implements Stringable. I've never really understood why, or why that=20
> interface even exists; but at least having a general concept of=20
> "implicit interface" would make it less magical.

__toString() is *old*.  It may go all the way back to 5.0, but it was th=
ere at least as of 5.2.  The problem is that there was no way to type ag=
ainst it.  You could type `string`, but not `string or object that imple=
ments string`.  When we got union types in 8.0, that was tempting but no=
t yet possible.  So Stringable was added basically for typing against `s=
tring|Stringable`.  And it was made implicitly added because there were =
a bajillion __toString() functions in the wild already that shouldn't ha=
ve to be modified before you could type against them.

</history lesson>

--Larry Garfield