Print debugging output only if some condition holds

[ffevotte]

@debug (and other logging macros like @info & co) are meant to log messages, so I’m not sure that’s what you want here.

The standard @assert is closer to what you’d want, but AFAIK it is not so easy to control whether checks are actually performed at run-time or not. So in your case, I’d probably use something like ToggleableAsserts – see the relevant discussion about this here on discourse:

@assert alternatives?

You can also look at taking advantage of constant propogation to get the behavior you want. asserting() = false #making this a function results in code being invalidated and recompiled when this gets changed macro mayassert(test) esc(:(if $(@__MODULE__).asserting() @assert($test) end)) end f(x) = @mayassert x < 2 If we use that in a function we can see it gets compile out julia> @code_llvm f(2) ; @ REPL[3]:1 within `f' define void @julia_f_12238(i64) { top: ret void } we can …

You example could be written something like (untested):

using ToggleableAsserts

function my_func(a::Int)
    @toggled_assert (a + 2 < 0)  "a + 2 cannot be negative"
    # Perform real calculation here.
    return a
end

And you can call toggle(true) or toggle(false) to decide whether you want checks to actually be performed (debug mode) or be elided (performance mode)