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for = vs for in normalization #34

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StefanKarpinski opened this issue Aug 14, 2019 · 11 comments
Closed

for = vs for in normalization #34

StefanKarpinski opened this issue Aug 14, 2019 · 11 comments

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@StefanKarpinski
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StefanKarpinski commented Aug 14, 2019 •
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The rule of thumb that I use for for loops is that if the thing you're iterating over is a literal range then you use = whereas if it's anything else (e.g. an object) then I use in. So, for example, these would be "correct":

for i = 1:n
    println(i)
end

for i in itr
    println(i)
end

These, on the other hand would be "incorrect":

for i in 1:n
    println(i)
end

for i = itr
    println(i)
end

Part of the reasoning is that for i = 1:n looks like it assigns i to 1, then 2, then ... n — at least in common mathematical / pseudocode notation, whereas for i = itr looks like it assigns i = itr which is not what it does. So one could argue "why use/allow for i = 1:n at all? Why not just use in uniformly and write for i in 1:n and for i in itr? Some people surely would prefer this. However, this superficial syntax difference can help catch a common error, which is writing for i = n when you meant to write for i = 1:n. If we require in there then the programmer will notice that for i in n is not what they meant to write and catch the bug.

So I would propose normalizing for = versus for in based on this rule. Thoughts?
@StefanKarpinski StefanKarpinski changed the title for = vs in normalization for = vs for in normalization Aug 14, 2019
@domluna
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domluna commented Aug 14, 2019 •
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I'm in favour of this.

Throwback https://github.com/julia-vscode/DocumentFormat.jl/pull/26/files#diff-8f8b649677f922163282f3d951be629aR89-R104.

Additionally this is a best practice for the prevalent style guides:

@domluna domluna mentioned this issue Aug 17, 2019
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@domluna domluna closed this as completed Aug 19, 2019
@domluna domluna mentioned this issue Sep 1, 2019
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@KwatMDPhD
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Good idea.

@diegozea
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diegozea commented Sep 3, 2019 •
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why use/allow for i = 1:n at all? Why not just use in uniformly and write for i in 1:n and for i in itr? Some people surely would prefer this.

I'm "some people" ;) I've found for = difficult to read, so I always use for in. I would prefer for ∈ instead of for = if a difference should be made.

@KwatMDPhD
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It's more difficult to type ∈. Also, ∈ is rarely found in other languages.

singularitti added a commit to MineralsCloud/QuantumESPRESSOBase.jl that referenced this issue Sep 10, 2019
@singularitti
style: Reformat code
82bfaad 
about why use `i = 1:nfields(data)` see:
domluna/JuliaFormatter.jl#34
@singularitti
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singularitti commented Sep 10, 2019 •
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I am "some people" also. In fact, some nonofficial guide has suggested not to use for ... = ....

@KwatMDPhD
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I'm for always using in.

PallHaraldsson added a commit to PallHaraldsson/YASGuide that referenced this issue Sep 11, 2019
@PallHaraldsson
Compatibility with formatter(s)
ffb7014 
Yes, you're more strict than Julia's style guide, that has this line:

for i = firstindex(a):lastindex(a)
uur guide
and Karpinski's reasoning here: domluna/JuliaFormatter.jl#34

I'm not sure I agree, but it's not good if the formatter generates style incompatible with guide(s). Your guide was updated in 2018 to reflect JuMP's but I at least didn't locate wording on this (yet) there.
@PallHaraldsson PallHaraldsson mentioned this issue Sep 11, 2019
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@odow
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odow commented Sep 11, 2019

Going to chime in on this dead issue that

Additionally this is a best practice for the prevalent style guides:

Is incorrect. JuMP's rule is to always prefer in over =.

Part of the reasoning is that for i = 1:n looks like it assigns i to 1, then 2, then ... n — at least in common mathematical / pseudocode notation, whereas for i = itr looks like it assigns i = itr which is not what it does.

You could (and I will) argume that i = 1:n looks like it assigns i to the iterable 1:n.

@KwatMDPhD
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https://github.com/jrevels/YASGuide also recommends using in over =. @domluna , is it difficult to update the code to use in instead of =?

@tk3369
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tk3369 commented Sep 15, 2019

I also opt for in over = in all circumstances although my visual cortex interprets them the same anyways. I love ∈ because it's cool but often it's just too much to type and so in wins.

@odow odow mentioned this issue Sep 16, 2019
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@Roger-luo
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Is there a way to choose different syntax guide? like this one. I also opt for in over = in all circumstances...

@StefanKarpinski
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No, there are currently no formatting options.

@domluna domluna mentioned this issue Oct 5, 2019
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8 participants
@StefanKarpinski @tk3369 @domluna @diegozea @KwatMDPhD @odow @Roger-luo @singularitti