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January 03, 2021 Recursively defined matcher function | ||||
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How can I define a function type `Matcher` that takes an array of `Matcher`s and returns an instance of a `struct Match` defined as struct Match { @safe pure nothrow @nogc: static Match zero() { return typeof(return)(0); } static Match none() { return typeof(return)(_length.max); } /// Match length in number of UTF-8 chars or 0 if empty. @property uint length() { return _length; } bool opCast(U : bool)() const { return _length != _length.max; } this(size_t length) { assert(length <= _length.max); this._length = cast(typeof(_length))length; } const uint _length; // length == uint.max is no match } I've tried alias Matcher = Match function(Matcher[] matchers...); but it errors as recursive alias declaration |
January 03, 2021 Re: Recursively defined matcher function | ||||
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Posted in reply to Per Nordlöw | On Sunday, 3 January 2021 at 18:26:44 UTC, Per Nordlöw wrote: > I've tried > > alias Matcher = Match function(Matcher[] matchers...); > > but it errors as > > recursive alias declaration The closest thing can I think of is: ``` alias matcherSignature(T:matcherSignature!T) = T (T[] matchers...); ``` I think we would require proper singleton types to model this as: ``` matcherSignature(matcherSignature.type[] matcherSignatures ...) ``` |
January 03, 2021 Re: Recursively defined matcher function | ||||
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Posted in reply to sighoya | On Sunday, 3 January 2021 at 18:49:40 UTC, sighoya wrote: > ``` > alias matcherSignature(T:matcherSignature!T) = T (T[] matchers...); > ``` > Ahhh, I meant this: ``` alias matcherSignature(T:matcherSignature!T) = Matcher (T[] matchers...); `` > I think we would require proper singleton types to model this as: > > ``` > matcherSignature(matcherSignature.type[] matcherSignatures ...) > ``` and this: ``` Matcher matcherSignature(matcherSignature.type[] matcherSignatures...) ``` |
January 03, 2021 Re: Recursively defined matcher function | ||||
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Posted in reply to sighoya | On Sunday, 3 January 2021 at 18:55:58 UTC, sighoya wrote: >``` >alias matcherSignature(T:matcherSignature!T) = Matcher (T[] matchers...); >``` Yet, it is right: ``` alias matcherSignature(T:matcherSignature!T) = Matcher function(T[] matchers...); ``` But it didn't work likewise, you have to instantiate it infinitely in nesting order. I think you either need some kind of nominalism to state matcherSignature!T exists for any T or you need to end it after a certain depth: ``` struct theEnd {} template matcherSignature(T) if (T==matcherSignature!T || T==theEnd) { Matcher function(T[] matchers...) fp; } ``` |
January 03, 2021 Re: Recursively defined matcher function | ||||
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Posted in reply to Per Nordlöw | On Sunday, 3 January 2021 at 18:26:44 UTC, Per Nordlöw wrote:
> alias Matcher = Match function(Matcher[] matchers...);
>
> but it errors as
>
> recursive alias declaration
Preferrably I wanted a non-templated definition.
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