Here is a small Fortran subroutine, with select case, subroutine steps(it) integer(kind=i8) :: it select case (imode) case (11) call step11(it) case (12) call step12(it) case default write (6,'(''Illegal imode value: '')') imode stop end select return end subroutine steps I wonder, …

Unfortunately not, you can do a sequence of if else statements and there might be some packages that do pattern matching, although if I would guess the if else statements are faster.

If I have many cases, just say 20 cases, it is a little difficult for me believe that if statements can be faster, because if I have to select the last case, I need to do like 19 if judges. Besides, the if else if else statements may be cumbersome somehow. But if there is a select case thing in Ju…

Seems pretty quick: julia> ex = :("last"); julia> for i in 50:-1:1 ex = :(x == $i ? $("value " * string(i)) : $ex) end julia> @eval f(x) = $ex f (generic function with 1 method) julia> @btime f(r[]) setup=(r=Ref(2)) 1.166 ns (0 allocations: 0 bytes) "value 2" julia> @btime f(…

It’s quick but much more confusing.

@mcabbott isn’t saying that’s how you should write them, he’s just generating a very large set of if statements (by metaprogramming) which will perform exactly the same as handwritten ones, and then showing those are fast (and therefore handwritten ones are as well).

[image] CRquantum: I need to do like 19 if judges. Besides, the if else if else statements may be cumbersome somehow Perhaps using a Dict would be more convenient where the case is the key and the call is the value?

I believe the kind of pattern you show up top will be compiled to a switch and then jump table (via Julia and LLVM respectively), much like I assume a Fortran compiler could. Edit: it doesn’t generate a jump table, but I wasn’t able to coax gfortran to create one either on Godbolt. If someone figur…

Thanks! This looks like a solid answer, although I am not very clear what does the script you displayed mean. But I believe Julia should be smart enough to do jumping instead of doing a lot of unnecessary if judgements. Just curious, why use ‘===’ in things like if it === 11 why not just use “=…

Perhaps to ensure it’s an integer. 12 === 12.0 evaluates as false. (If you want info on the operator use ?=== in the REPL).

Is there a "select case" equivalent in Julia?

General Usage

greg_plowman August 16, 2021, 11:00pm 3

The discussion here might be relevant: A switch type function

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Is there a "select case" equivalent in Julia?

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