Maybe this is a dumb question, but there seems to be a bit of confusion about using ismissing(x) versus x === missing, and isnothing(x) versus x === nothing at [ANN] ShowLint - #3 by Mason . I would say that in both cases, the functions are clearer for new Julia users. This is supported by the docum…

[image] rikh: So, is it right that ismissing and isnothing is prefered except when you need to squeeze every last bit of performance? Using === (or !==) allows the compiler to disregard the other alternative type if the inferred type is e.g. a Union{Nothing, T}. Using == or isnothing does no…

I’ve replied to this at [ANN] ShowLint - #11 by rikh .

[image] joa-quim: it would be another annoying red mark in the code when opened in VSC. @joa-quim To clarify, the linter that @rikh has created is separate from the linter that is built into the Julia VS Code extension.

[image] kristoffer.carlsson: Using == or isnothing does not allow this. Is that because if x is of type T (rather than Nothing), isnothing(x) might not return a boolean value? In other words, isnothing(x::T) might be overloaded to not return a boolean? Or perhaps isnothing(x::T) is overloaded…

Sorry for my dumb addition. I use this in my packages for Julia 1.0 compat (which is the implementation in Julia 1.1+): isnothing(::Any) = false isnothing(::Nothing) = true So actually, this: @inline isnothing(x) = x === nothing would be the more performant (compiler friendly) version which has …

[image] tamasgal: So actually, this: @inline isnothing(x) = x === nothing would be the more performant (compiler friendly) version which has no drawbacks. No, it has to be === at every call site in the code. As soon as you hide it behind a function, you’ve lost the === advantage.

Even if it’s inlined? :thinking:

[image] kristoffer.carlsson: As soon as you hide it behind a function, you’ve lost the === advantage. This is rather confusing, because Julia is often advertised as having “zero cost abstractions”.

[image] tamasgal: Even if it’s inlined? :thinking: Yes. [image] CameronBieganek: This is rather confusing, because Julia is often advertised as having “zero cost abstractions”. [CppCon 2019: Chandler Carruth “There Are No Zero-cost Abstractions”] :wink: As already been s…

Are there really no zero-cost abstractions? I thought some abstractions ‘compiled away’ to produce the same machine code as the ‘inline’ code (like in inlined functions). Are you including compilation cost?

Ismissing(x) versus x === missing

General Usage

joa-quim December 21, 2020, 1:45pm 3

But Lint is not for new users only. I don’t think isnothing(x) should be advised against x === nothing. I have no intention to follow the suggestion and it would be another annoying red mark in the code when opened in VSC.

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Ismissing(x) versus x === missing

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