Hello!
equals() spec says:
The implicitly provided implementation returns {@code true} if
and * only if the argument is an instance of the same record type
as this object, * and each component of this record is equal to
the corresponding component * of the argument, according to {@link
Object#equals(Object)} for components * whose types are reference
types, and {@code ==} for components whose * types are primitive
types. *
This contradicts the class spec for float/double fields (in
particular, NaN values):
* <p>For all record classes, the following invariant must hold: if a
record R's * components are {@code c1, c2, ... cn}, then if a record
instance is copied * as follows: * <pre> * R copy = new R(r.c1(),
r.c2(), ..., r.cn()); * </pre> * then it must be the case that {@code
r.equals(copy)}.
E.g.
record R(double d) {}
R r1 = new R(Double.NaN);
R r2 = new R(r1.d());
assert r1.equals(r2); // fails as R.d is a primitive field and r1.d != r2.d
With best regards,
Tagir Valeev.
On Fri, Aug 16, 2019 at 12:15 AM Tagir Valeev <[email protected]> wrote:
> Hello!
>
> >a private static field corresponding to each component
>
> Final instead of static?
>
> With best regards,
> Tagir Valeev
>
> пт, 16 авг. 2019 г., 0:06 Brian Goetz <[email protected]>:
>
>> Draft spec, please comment.
>>
>>
>> /* * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
>> * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This
>> code is free software; you can redistribute it and/or modify it * under the
>> terms of the GNU General Public License version 2 only, as * published by
>> the Free Software Foundation. Oracle designates this * particular file as
>> subject to the "Classpath" exception as provided * by Oracle in the LICENSE
>> file that accompanied this code. * * This code is distributed in the hope
>> that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied
>> warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the
>> GNU General Public License * version 2 for more details (a copy is included
>> in the LICENSE file that * accompanied this code). * * You should have
>> received a copy of the GNU General Public License version * 2 along with
>> this work; if not, write to the Free Software Foundation, * Inc., 51
>> Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact
>> Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit
>> www.oracle.com if you need additional information or have any * questions.
>> */package java.lang;
>> /** * This is the common base class of all Java language record classes. * *
>> <p>More information about records, including descriptions of the *
>> implicitly declared methods synthesized by the compiler, can be * found in
>> section 8.10 of * <cite>The Java™ Language Specification</cite>. * *
>> <p>A <em>record class</em> is a shallowly immutable, transparent carrier for
>> * a fixed set of values, called the <em>record components</em>. The
>> Java™ * language provides concise syntax for declaring record classes,
>> whereby the * record components are declared in the record header. The list
>> of record * components declared in the record header form the <em>record
>> descriptor</em>. * * <p>A record class has the following mandated members: a
>> public <em>canonical * constructor</em>, whose descriptor is the same as the
>> record descriptor; * a private static field corresponding to each component,
>> whose name and * type are the same as that of the component; a public
>> accessor method * corresponding to each component, whose name and return
>> type are the same as * that of the component. If not explicitly declared in
>> the body of the record, * implicit implementations for these members are
>> provided. * * <p>The implicit declaration of the canonical constructor
>> initializes the * component fields from the corresponding constructor
>> arguments. The implicit * declaration of the accessor methods returns the
>> value of the corresponding * component field. The implicit declaration of
>> the {@link Object#equals(Object)}, * {@link Object#hashCode()}, and {@link
>> Object#toString()} methods are derived * from all of the component fields. *
>> * <p>The primary reasons to provide an explicit declaration for the *
>> canonical constructor or accessor methods are to validate constructor *
>> arguments, perform defensive copies on mutable components, or normalize
>> groups * of components (such as reducing a rational number to lowest terms.)
>> If any * of these are provided explicitly. * * <p>For all record classes,
>> the following invariant must hold: if a record R's * components are {@code
>> c1, c2, ... cn}, then if a record instance is copied * as follows: * <pre> *
>> R copy = new R(r.c1(), r.c2(), ..., r.cn()); * </pre> * then it must be
>> the case that {@code r.equals(copy)}. * * @jls 8.10 * @since 14 */public
>> abstract class Record {
>> /** * Indicates whether some other object is "equal to" this one.
>> In addition * to the general contract of {@link Object#equals(Object)},
>> * record classes must further participate in the invariant that when
>> * a record instance is "copied" by passing the result of the record
>> component * accessor methods to the canonical constructor, the resulting
>> copy is * equal to the original instance. * * @implNote *
>> The implicitly provided implementation returns {@code true} if and *
>> only if the argument is an instance of the same record type as this object,
>> * and each component of this record is equal to the corresponding
>> component * of the argument, according to {@link Object#equals(Object)}
>> for components * whose types are reference types, and {@code ==} for
>> components whose * types are primitive types. * * @see
>> Object#equals(Object) * * @param obj the reference object with
>> which to compare. * @return {@code true} if this object is the same as
>> the obj * argument; {@code false} otherwise. */
>> @Override public abstract boolean equals(Object obj);
>>
>> /** * {@inheritDoc} * * @implNote * The implicitly
>> provided implementation returns a hash code value derived * by combining
>> the hash code value for all the components, according to * {@link
>> Object#hashCode()} for components whose types are reference types, * or
>> the primitive wrapper hash code for components whose types are primitive
>> * types. * * @see Object#hashCode() * * @return a
>> hash code value for this object. */ @Override public abstract int
>> hashCode();
>>
>> /** * {@inheritDoc} * * @implNote * The implicitly
>> provided implementation returns a string that is derived * from the name
>> of the record class and the names and string representations * of all
>> the components, according to {@link Object#toString()} for components *
>> whose types are reference types, and the primitive wrapper {@code toString}
>> * method for components whose types are primitive types. * * @see
>> Object#toString() () * * @return a string representation of the
>> object. */ @Override public abstract String toString();
>> }
>>
>>
