Is *explicit* better than implicit?

[szaghi]

I feel that there is an almost unanimous agreement on that implicit none must be mandatory, but I guess many of you will provide interesting exceptions, so

do you agree to advice to be explicit?

In the case you disagree, please elaborate your idea.

[cmacmackin]

I can think of no circumstance in which explicit none should be
omitted. Put it at the start of every module, submodule, or program.

On 16-01-18 04:35 PM, Stefano Zaghi wrote:

I feel that there is an almost unanimous agreement on that |implicit
none| must be mandatory, but I guess many of you will provide
interesting /exceptions/, so

do you agree to advice to be explicit?

In the case you disagree, please elaborate your idea.

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#10.

Chris MacMackin
cmacmackin.github.io http://cmacmackin.github.io

[LadaF]

I think implicit none can be omitted for procedures which get implicit none from their host, both internal and module procedures. At least that
is my personal style and I omit it in this case always.

2016-01-18 16:36 GMT+00:00 Chris MacMackin notifications@github.com:

I can think of no circumstance in which explicit none should be
omitted. Put it at the start of every module, submodule, or program.

On 16-01-18 04:35 PM, Stefano Zaghi wrote:

I feel that there is an almost unanimous agreement on that |implicit
none| must be mandatory, but I guess many of you will provide
interesting /exceptions/, so

do you agree to advice to be explicit?

In the case you disagree, please elaborate your idea.

—
Reply to this email directly or view it on GitHub
#10.

Chris MacMackin
cmacmackin.github.io http://cmacmackin.github.io

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#10 (comment)
.

[cmacmackin]

Agreed. So long as they are within a scope in which implicit none has
been specified. (Hence why I didn't list functions and subroutines as
places where it should be specified.)

On 16-01-18 04:41 PM, LadaF wrote:

I think implicit none can be omitted for procedures which get implicit none from their host, both internal and module procedures. At least that
is my personal style and I omit it in this case always.

2016-01-18 16:36 GMT+00:00 Chris MacMackin notifications@github.com:

I can think of no circumstance in which explicit none should be
omitted. Put it at the start of every module, submodule, or program.

On 16-01-18 04:35 PM, Stefano Zaghi wrote:

I feel that there is an almost unanimous agreement on that |implicit
none| must be mandatory, but I guess many of you will provide
interesting /exceptions/, so

do you agree to advice to be explicit?

In the case you disagree, please elaborate your idea.

—
Reply to this email directly or view it on GitHub

#10.

Chris MacMackin
cmacmackin.github.io http://cmacmackin.github.io

—
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#10 (comment)
.

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#10 (comment).

Chris MacMackin
cmacmackin.github.io http://cmacmackin.github.io

[szaghi]

@LadaF sure, I agree: in those cases it is unnecessary, but my question was, indeed,

have some of you good reasons to use implicit defined variables (as the older of us learned to do with F66/77)?

[LadaF]

There are some tricks for poor man's templates where instead of C macros one can use implicit typing and standard include statement.

consider

#define mytype type(abc)
subroutine abc_sub
#include "sub_base-inc-1.f90"
end subroutine
#undef mytype

with "sub_base-inc-1.f90" containing

mytype :: var

versus

subroutine abc_sub
    implicit type(abc) (v)
    include "sub_base-inc-2.f90"
end subroutine

with "sub_base-inc.f90" containing just the usage of variable var. I am not sure if I got the implicit statement completely right, as I never use it.

[nncarlson]

Very interesting trick @LadaF. Not sure I'd ever use it, but it's interesting nonetheless.

I'd go a step beyond making implicit none mandatory at the start of any module or program. I'd also require that it not appear at the start of any module or internal procedure which get it from their host. Programmers learn by example and the takeaway message by having it there is that it must be necessary somehow, and mislead an unaware programmer.

[szaghi]

@LadaF thank you very much, I win my bet, I guessed that I can learn something even by implicit! I love to learn something new that I never read, your trick is very appreciated!

@nncarlson I am sorry, but I completely miss your point. Can you elaborate more on not appear at the start of...?

[nncarlson]

@szaghi, If implicit none is present at the start of a module (and I think it should be required) then it applies to the entire module scope and it is not necessary to put it also at the start of the contained procedures, as others have noted. One can go ahead anyway and add implicit none at the start of contained procedures, but it is redundant and unnecessary, and conveys the false idea that it is required. For those reasons I'd require that implicit none not be declared there, but only at the module/program scope. As I said, programmers learn by example.

[cmacmackin]

I second requiring it not to be declared at the start of internal/module
procedures.

On 16-01-18 09:50 PM, Neil Carlson wrote:

@szaghi https://github.com/szaghi, If implicit none is present at
the start of a module (and I think it should be required) then it
applies to the entire module scope and it is not necessary to put it
also at the start of the contained procedures, as others have noted.
One can go ahead anyway and add implicit none at the start of
contained procedures, but it is redundant and unnecessary, and conveys
the false idea that it is required. For those reasons I'd require that
implicit none not be declared there, but only at the module/program
scope. As I said, programmers learn by example.

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[raullaasner]

This could be part of a general rule: do not write code that has no effect. The implicit none scope is an example of where such a rule is not self-evident, for beginners at least.

[szaghi]

@nncarlson and all, sorry, this was so obvious for me that I was confused before reach the second, crucial, argument that @raullaasner clarifies

do not write code that has no effect

Wonderful, great zen! Thank you very much.

[nncarlson]

@raullaasner is spot on with the general rule. Another example that comes to mind (sorry drifting off-topic) is deallocation of local allocatable variables. Don't bother with explicitly deallocating them before returning to the caller -- it happens automatically. Explicitly deallocating them conveys the false notion to the naive that it is necessary to avoid memory leaks.

[raullaasner]

@nncarlson If you want to check the deallocation status and catch any error messages, you would need to do that manually.

[nncarlson]

@raullaasner, that's true of course. I'm curious though who actually checks the deallocation status, and have they ever seen a deallocation failure. But don't answer! -- a topic for a different thread when the time is ripe (make a note @szaghi :-)