Feature request: {=} alias for issetequal

[ParadaCarleton]

As title says; issetequal is a bit long to type out and is unintuitive as a comparison operator, since statements like x==y are usually written with infix notation. {=} (or perhaps {==}) should be intuitive, and it saves time when typing. Similarly, x {!==} y and x {≠} y would be great for set inequality. The latter would also be nice performance improvements over the current practice of using !issetequal(), since it allows for short-circuit style evaluation: As soon as the function finds some element of x that is not an element of y, we can stop checking whether any other elements are in x but not y, since we have already proven the two sets are not equal by counterexample.

[oscardssmith]

Allowing braces as part of an identifier seems like a really bad decision.

[ParadaCarleton]

Allowing braces as part of an identifier seems like a really bad decision.

Maybe; what would you propose instead?

[oscardssmith]

I don't think this should have an ASCII symbol only alias.

[JeffBezanson]

If there is a standard mathematical symbol for this that's in unicode, we should use that, but I don't think one exists.

[ParadaCarleton]

If there is a standard mathematical symbol for this that's in unicode, we should use that, but I don't think one exists.

How about using ≃ for equivalence relations in general, and then specifying the desired equivalence relation with a keyword like under? For example, these would return true:

4 ≃ 2 under mod(2)

[1, 2, 3] ≃ [3, 1, 2] under seteq

[StefanKarpinski]

You can, in your own code, pick a infix Unicode operator and just use it. E.g.:

julia> const ≃ = issetequal
issetequal (generic function with 4 methods)

julia> [1, 2] ≃ [2, 1, 2]
true

This just isn't an operation that gets used enough to need special syntax for it. I do this sometimes when I'm writing code that does a lot of set differences with const \ = setdiff.

[ivaquero]

Hi, @StefanKarpinski, I just tried your method

const ∖ = setdiff

However, I got an error message

LoadError: syntax: invalid character "∖" near column 7
syntax: invalid character "∖" near column 7

Stacktrace:
 [1] top-level scope
   @ In[37]:1
 [2] eval
   @ ./boot.jl:360 [inlined]
 [3] include_string(mapexpr::typeof(REPL.softscope), mod::Module, code::String, filename::String)
   @ Base ./loading.jl:1116

How can I fix this ? BTW, I use Julia 1.6.2 in Jupyter. I guess it is a problem of \setminus Unicode because const ≃ = issetequal works.

[cormullion]

Notice the different Unicode values of the two glyphs:

[ivaquero]

I see, thanks. Another question, what caused the \setminus Unicode ocupied ? Why cannot it be used here ?