[almighty] Equaler considered harmful

[Andrew Lee Rubinger]

Java may have made an odd design design by putting "boolean equals(Object)"
in the root Object class as a mechanism to test equality by value, but
there's also:

  https://docs.oracle.com/javase/8/docs/api/java/lang/Comparable.html

This approach handles not just equals but also greater/less than
comparisons for types that have ordered values.  You could retrofit it to
return an enum type instead of an int for better clarity.

Something to consider :)

S,
ALR

On Thu, Sep 22, 2016 at 10:19 AM, Konrad Kleine <kkleine at redhat.com> wrote:

> Hi Thomas,
>
> thanks for not pointing in my direction :)
>
> I can't wait to see a PR for this.
>
> Regards,
> Konrad
>
> On Thu, Sep 22, 2016 at 3:32 PM, Thomas Mäder <tmader at redhat.com> wrote:
>
>> Hi folks,
>>
>> some time back, we have introduced the "Equaler" interface. I believe
>> we're going down the wrong path with this: Java got this wrong initially
>> and we still suffer the consequences. Equaler looks like this:
>>
>> type Equaler interface {
>>     Equal(Equaler) bool
>> }
>>
>> There are a couple of drawbacks to this approach:
>>
>>    1. There can only be a single implementation of Equals for all time.
>>    But this too restrictive: for example, I might want to include the version
>>    field in a struct in the comparison for some cases, in other cases I simply
>>    don't care. Generally, there can be many equivalence relationships for a
>>    given set of objects. For all we know, we might consider two objects equal
>>    if they have the same color.
>>    2. You can't compose equality with this implementation
>>    In Java, this has given rise to classes like "EqualsBuilder" that
>>    allowed to do exactly that.
>>    3. We can't implement equality based on interfaces
>>    We'd have to reimplement equality for every struct (which is the
>>    first parameter).
>>    4. You always have to check for null before calling Equals()
>>
>> So I propose to rewrite the interface to :
>>
>> Equality {
>>
>>     Equals(left interface{}, right interface{}) bool
>>
>> }
>>
>> I think it would make sense that I prepare a PR to illustrate my approach
>> porting the current implementations in the "models" packe. A POC shouldn't
>> take too long.
>>
>> thoughts?
>>
>> /Thomas
>>
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>>
>
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