Can I give a reference? Well, I did: the ANSI Smalltalk standard. Specifically, section 5.7.8.2, the refinement for <sequenceReadableCollection>
Numbers are governed by section 5.6.7.1, which requires numbers that are compared for equality to be converted to a common representation, which in this case requires (sigh) integers to be converted to floats. With that definition it is possible to find integers x z and a float y such that x = y and y = z are true but x = z is false, which is a very bad thing. My Smalltalk tries to be ANSI conformant, but some things are just too broken to live with, and that's one of them. (The rule should always be to convert in a way that loses no information.) It may well seem strange to you, but "equivalence" (#=) in Smalltalk is not coupled to "ordering" (the Magnitude methods) and never has been. For example, #= compares the characters of strings, which are equal iff they have the same codepoint. But #< and the other magnitude methods use an "implementation-defined" collation order, which could, for example, ignore alphabetic case. So it would be entirely consistent with the standard and historic practice to have 'A' <= 'a' and 'a' <= 'A' but 'A' ~= 'a'. This is not merely a theoretical possibility; I just tried it in GNU Smalltalk. There was a serious historic bug in many Smalltalks where 'a' = #a was true (using string comparison) but #a = 'a' was false (using identity). This may well be why the standard insists on the classes (not the species) being the same, to ensure that <string> = <symbol> is consistent with <symbol> = <string>. On 1 August 2018 at 16:47, James Foster <[email protected]> wrote: > @Richard O’Keefe: I’m trying to find the place in the ANSI Standard you > are citing. All I’ve found so far is at 5.3.1.1: > > The meaning of "equivalent" cannot be precisely defined but the intent is > that two objects are > considered equivalent if they can be used interchangeably. Conforming > protocols may choose to > more precisely define the meaning of "equivalent”. > > Can you provide a reference for your assertion that objects must be of the > same class in order to be equivalent? > > How about other comparisons between objects of different classes? Is 1.9 < > 2? Is 2.1 > 2? How about 2.0 = 2? Is #a < ‘b’? is #b > ‘a’? How about #a = > ‘a’? It seems strange to suggest that an object can be less than or greater > than, but not equal to! > > James > > On Jul 31, 2018, at 9:24 PM, Richard O'Keefe <[email protected]> wrote: > @James Foster: 100%. There are no exceptions > > On 1 August 2018 at 02:05, James Foster <[email protected]> wrote: > >> To what extent is it required by ANSI that objects be of the same class? >> >
