Quick example of @BoundsCheck from the Julia REPL

Readme.md

https://docs.julialang.org/en/v1.0/base/base/#Base.@boundscheck

https://docs.julialang.org/en/v1.0/devdocs/boundscheck/#Bounds-checking-1

JuliaCon 2016 | Bounds Check Elimination | Blake Johnson https://www.youtube.com/watch?v=4XorFlvQEiI

boundscheck_example.jl

@inline function a(perm, array)
   @boundscheck begin
       println("trying a boundscheck")
       min, max = extrema(perm)
       checkbounds(array, min)
       checkbounds(array, max)
       println("did a bounds check successfully")
   end    
   println("done")
end

function b(do_check, perm, array)
   if do_check     
     a(perm, array)
   else
     println("No bounds check")
     @inbounds a(perm, array)
   end
end


julia> b(true, [1,2,5], [5,5,5])
trying a boundscheck
ERROR: BoundsError: attempt to access 3-element Array{Int64,1} at index [5]
Stacktrace:
 [1] throw_boundserror(::Array{Int64,1}, ::Tuple{Int64}) at ./abstractarray.jl:434
 [2] checkbounds at ./abstractarray.jl:362 [inlined]
 [3] a at ./REPL[39]:6 [inlined]
 [4] b(::Bool, ::Array{Int64,1}, ::Array{Int64,1}) at ./REPL[47]:3

julia> b(false, [1,2,5], [5,5,5])
No bounds check
done

example_from_julia_essentials.jl

# https://docs.julialang.org/en/v1.0/base/base/#Base.@boundscheck

julia> @inline function g(A, i)
           @boundscheck checkbounds(A, i)
           return "accessing ($A)[$i]"
       end;

julia> f1() = return g(1:2, -1);

julia> f2() = @inbounds return g(1:2, -1);

julia> f1()
ERROR: BoundsError: attempt to access 2-element UnitRange{Int64} at index [-1]
Stacktrace:
 [1] throw_boundserror(::UnitRange{Int64}, ::Tuple{Int64}) at ./abstractarray.jl:455
 [2] checkbounds at ./abstractarray.jl:420 [inlined]
 [3] g at ./none:2 [inlined]
 [4] f1() at ./none:1
 [5] top-level scope

julia> f2()
"accessing (1:2)[-1]"