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[CLJ-1333] Documentation for "=" is misleading Created: 30/Jan/14  Updated: 14/Feb/14

Status: Open
Project: Clojure
Component/s: None
Affects Version/s: Release 1.5
Fix Version/s: None

Type: Enhancement Priority: Minor
Reporter: George Assignee: Unassigned
Resolution: Unresolved Votes: 0
Labels: docs
Environment:

linux 2.6.32-431.el6.x86_64


 Description   

Document for clojure.core/= says it compares numbers in a type-independent manner. In reality the comparission is made in a type dependent manner. If the above statement was true then (= 1 1.0) would eval to true not false;

clojure.core/=
([x] [x y] [x y & more])
Equality. Returns true if x equals y, false if not. Same as
Java x.equals except it also works for nil, and compares
numbers and collections in a type-independent manner. Clojure's immutable data
structures define equals() (and thus =) as a value, not an identity,
comparison.

 Comments   
Comment by Kevin Downey [ 02/Feb/14 4:58 PM ]

I think this is a little more complex than described.

= does compare things in a jvm type independent manner, but it does use what people have taken to calling "equality classes"

(= [1 2] '(1 2))

(= {:a 1} (doto (java.util.HashMap.) (.put :a 1)))

etc.

now for numbers, it seems logical to me, to have floating point and precise numbers in distinct equality classes

in which case, 1.0 and 1 are in distinct equality classes, so not equal.

Comment by Gary Fredericks [ 13/Feb/14 10:16 PM ]

The docstring is definitely misleading for people unfamiliar with this sort of thing though. Numbers are probably the first thing that the words "type independent manner" bring to mind. A brief pointer to the == function might be useful.

Comment by George [ 14/Feb/14 5:47 AM ]

I find == function to be confusing
For example
(== 1 1.0) => true
(== 1 1.0M) => false ; what is wrong with this comparison?

and doc says:
Returns non-nil if nums all have the equivalent value (type-independent)

Comment by Alex Miller [ 14/Feb/14 7:56 AM ]

@George - that last example (== 1 1.0M) is actually a bug that is fixed in 1.6 where it will return true.

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