On Wed, Apr 22, 2020 at 11:10 PM Barney Laurance <bar...@redmagic.org.uk> wrote: > > The union of all other types is the top type, but I think as used in phpDoc > mixed is often really a dynamic type, rather than a top type. > > The top type (e.g. Typescript's 'unknown') is the supertype of all other > types, > while the dynamic type (e.g. Typescripts 'any') is simultaneously a > supertype > and a subtype of all other types.
In Typescript (statically typed), both `any` and `unknown` are "supertype", but the former basically disables compile-time type checking (and opens for runtime errors) while the latter requires you write type checks/assertions. I guess `undefined` would be the actual "subtype". (By the way, unlike PHP, Typescript considers `void` a data type, i.e. you can have a "void variable" and assign it the value `undefined`.) Anyway, <https://docs.phpdoc.org/latest/guides/types.html> defines `mixed` as "A value with this type can be literally anything; the author of the documentation is unable to predict which type it will be" (even if some also use it where a union of a subset of types would be more accurate). > Taking a random example, arguments to str_replace documented as mixed > accept string|array and not anything else. Indeed, <https://www.php.net/manual/en/language.pseudo-types.php#language.types.mixed> currently says that, in the PHP documentation, "`mixed` indicates that a parameter may accept multiple (but not necessarily all) types", and gives two examples: <https://www.php.net/manual/en/function.gettype.php> is accurate, but <https://www.php.net/manual/en/function.str-replace.php> IMO should just use `string|array` rather than `mixed` (that's already the case in <https://github.com/php/php-src/blob/master/ext/standard/basic_functions.stub.php#L649-L655>). > So maybe the LSP rules shouldn't apply as described in the RFC to mixed. If > str_replace was a class method it might be OK for a subclass to change the > param type to e.g. array|string|int. > > That would leave scope for adding a real top type in a later RFC. I'd rather have the docs "fixed" (but I suspect `str_replace` is not the only place where `mixed` is used in an "approximate" fashion). `mixed` as defined by this RFC (i.e. equivalent to the currently-impossible-to-write union of all primitive types, including resource and null [but not void that is not a data type]) is LSP-conformant. Regards, -- Guilliam Xavier -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
