S7 0.1.1

Classes get a more informative print method (#346).
Correctly register S3 methods for S7 objects with a package (#333).
External methods are now registered using an attribute of the S3 methods table rather than an element of that environment. This prevents a warning being generated during the “code/documentation mismatches” check in R CMD check (#342).
class_missing and class_any can now be unioned with | (#337).
new_object() no longer accepts NULL as .parent.
new_object() now correctly runs the validator from abstract parent classes (#329).
new_object() works better when custom property setters modify other properties.
new_property() gains a validator argument that allows you to specify a per-property validator (#275).
new_property() clarifies that it’s the user’s responsibility to return the correct class; it is not automatically validated.
Properties with a custom setter are now validated after the setter has run and are validated when the object is constructed or when you call validate(), not just when you modify them after construction.
S7_inherits() now accepts class = NULL to test if an object is any sort of S7 object (#347).

S7 0.1.0

new_external_generic() is only needed when you want a soft dependency on another package.
methods_register() now also registers S3 and S4 methods (#306).

Subclasses of abstract class can have readonly properties (#269).
During construction, validation is now only performed once for each element of the class hierarchy (#248).
Implemented a better filtering strategy for the S4 class hierarchy so you can now correctly dispatch on virtual classes (#252).
New set_props() to make a modified copy of an object (#229).
R CMD check now passes on R 3.5 and greater (for tidyverse compatibility).
Dispatching on an evaluated argument no longer causes a crash (#254).
Improve method dispatch failure message (#231).
Can use | to create unions from S7 classes (#224).
Can no longer subclass an environment via class_environment because we need to think the consequences of this behaviour through more fully (#253).

Add [.S7_object, [<-.S7_object, [[.S7_object, and [[<-.S7_object methods to avoid “object of type ‘S4’ is not subsettable” error (@jamieRowen, #236).
Combining S7 classes with c() now gives an error (#230)
Base classes now show as class_x instead of "x" in method print (#232)

Exported class_factor, class_Date, class_POSIXct, and class_data.frame.
New S7_inherits() and check_is_S7() (#193)
new_class() can create abstract classes (#199).
method_call() is now S7_dispatch() (#200).
Can now register methods for double-dispatch base Ops (currently only works if both classes are S7, or the first argument is S7 and the second doesn’t have a method for the Ops generic) (#128).
All built-in wrappers around base types use class_. You can no longer refer to a base type with a string or a constructor function (#170).
convert() allows you to convert an object into another class (#136).
super() replaces next_method() (#110).

class_any and class_missing make it possible to dispatch on absent arguments and arguments of any class (#67).
New method_explain() to explain dispatch (#194).
Minor property improvements: use same syntax for naming short-hand and full property specifications; input type automatically validated for custom setters. A property with a getter but no setter is read-only (#168).
When creating an object, unspecified properties are initialized with their default value (#67). DISCUSS: to achieve this, the constructor arguments default to class_missing.
Add $.S7_object and $<-.S7_object methods to avoid “object of type ‘S4’ is not subsettable” error (#204).
Dispatch now disambiguates between S4 and S3/S7, and, optionally, between S7 classes in different packages (#48, #163).
new_generic() now requires dispatch_args (#180). This means that new_generic() will typically be called without names. Either new_generic("foo", "x") for a “standard” generic, or new_generic("foo", "x", function(x, y) call_method()) for a non-standard method.
new_external_generic() now requires dispatch_args so we can eagerly check the signature.
Revamp website. README now shows brief example and more info in vignette("S7"). Initial design docs and minutes are now articles so they appear on the website.

New props<- for setting multiple properties simultaneously and validating afterwards (#149).
Validation now happens recursively, and validates types before validating the object (#149)
Classes (base types, S3, S4, and S7) are handled consistently wherever they are used. Strings now only refer to base types. New explicit new_S3_class() for referring to S3 classes (#134). S4 unions are converted to S7 unions (#150).
Base numeric, atomic, and vector “types” are now represented as class unions (#147).
Different evaluation mechanism for method dispatch, and greater restrictions on dispatch args (#141)
x@.data -> S7_data(); probably to be replaced by casting.
In generic, signature -> dispatch_args.
Polished str() and print() methods
new_class() has properties as 3rd argument (instead of constructor).